1 Introduction

1.1 Why Should I use Kerberos?

Since Kerberos negotiates authenticated, and optionally encrypted,
communications between two points anywhere on the internet, it provides
a layer of security that is not dependent on which side of a firewall
either client is on. Since studies have shown that half of the computer
security breaches in industry happen from inside firewalls,
Kerberos V5 from MIT will play a vital role in the
security of your network.

1.2 Documentation for Kerberos V5

This document is one piece of the document set for Kerberos V5. The
documents, and their intended audiences, are:

Kerberos V5 Installation Guide: a concise guide for installing
Kerberos V5. Kerberos administrators (particularly whoever will be
making site-wide decisions about the installation) and the system
administrators who will be installing the software should read this
guide.

Kerberos V5 System Administrator's Guide: a sysadmin's guide to
administering a Kerberos installation. The System Administrator's Guide
describes the administration software and suggests policies and
procedures for administering a Kerberos installation. Anyone who will
have administrative access to your Kerberos database should read this
guide.

Kerberos V5 UNIX User's Guide: a guide to using the Kerberos
UNIX client programs. All users on UNIX systems should read this guide,
particularly the “Tutorial” section.

2 How Kerberos Works

This section provides a simplified description of a general user's
interaction with the Kerberos system. This interaction happens
transparently—users don't need to know and probably don't care about
what's going on—but Kerberos administrators might find a schematic
description of the process useful. This description glosses over a lot
of details; for more information, see Kerberos: An Authentication
Service for Open Network Systems, a paper presented at Winter USENIX
1988, in Dallas, Texas. This paper can be retreived by FTP from
athena-dist.mit.edu, in the location:
/pub/ATHENA/kerberos/doc/usenix.PS.

2.1 Network Services and Their Client Programs

In an environment that provides network services, you use client
programs to request services from server programs that are
somewhere on the network. Suppose you have logged in to a workstation
and you want to ‘rlogin’ to a typical UNIX host. You use the local
‘rlogin’ client program to contact the remote machine's
‘rlogind’ daemon.

2.2 Kerberos Tickets

Under Kerberos, the ‘klogind’ daemon allows you to login to a
remote machine if you can provide ‘klogind’ a Kerberos ticket
which proves your identity. In addition to the ticket, you must also
have possession of the corresponding ticket session key. The
combination of a ticket and the ticket's session key is known as a credential.

Typically, a client program automatically obtains credentials
identifying the person using the client program. The credentials are
obtained from a Kerberos server that resides somewhere on the network.
A Kerberos server maintains a database of user, server, and password
information.

2.3 The Kerberos Database

Kerberos will give you credentials only if you have an entry in the
Kerberos server's Kerberos database. Your database entry includes
your Kerberos principal (an identifying string, which is often
just your username), and your Kerberos password. Every Kerberos user
must have an entry in this database.

2.4 Kerberos Realms

Each administrative domain will have its own Kerberos database, which
contains information about the users and services for that particular
site or administrative domain. This administrative domain is the
Kerberos realm.

Each Kerberos realm will have at least one Kerberos server, where the
master Kerberos database for that site or administrative domain is
stored. A Kerberos realm may also have one or more slave servers,
which have read-only copies of the Kerberos database that are
periodically propagated from the master server. For more details on how
this is done, see the “Set Up the Slave KDCs for Database Propagation”
and “Propagate the Database to Each Slave KDC” sections of the
Kerberos V5 Installation Guide.

2.5 The Ticket-Granting Ticket

The ‘kinit’ command prompts for your password. If you enter it
successfully, you will obtain a ticket-granting ticket and a
ticket session key which gives you the right to use the ticket.
This combination of the ticket and its associated key is known as your
credentials. As illustrated below, client programs use your
ticket-granting ticket credentials in order to obtain client-specific
credentials as needed.

Your credentials are stored in a credentials cache, which is often
just a file in /tmp. The credentials cache is also called the
ticket file, especially in Kerberos V4 documentation. Note,
however, that a credentials cache does not have to be stored in a file.

2.6 Network Services and the Master Database

The master database also contains entries for all network services that
require Kerberos authentication. Suppose that your site has a machine,
‘laughter.mit.edu’, that requires Kerberos
authentication from anyone who wants to ‘rlogin’ to it. The host's
Kerberos realm is ‘ATHENA.MIT.EDU’.

This service must be registered in the Kerberos database, using the
proper service name, which in this case is the principal:

host/laughter.mit.edu@ATHENA.MIT.EDU

The ‘/’ character separates the Kerberos primary (in this
case, ‘host’) from the instance (in this case,
‘laughter.mit.edu’); the ‘@’ character separates
the realm name (in this case, ‘ATHENA.MIT.EDU’) from the rest
of the principal. The primary, ‘host’, denotes the name or type of
the service that is being offered: generic host-level access to the
machine. The instance, ‘laughter.mit.edu’, names the
specific machine that is offering this service. There will generally be
many different machines, each offering one particular type of service,
and the instance serves to give each one of these servers a different
Kerberos principal.

2.6.1 The Keytab File

For each service, there must also be a service key known only by
Kerberos and the service. On the Kerberos server, the service key is
stored in the Kerberos database.

On the server host, these service keys are stored in key tables,
which are files known as keytabs.1 For example, the service keys used by
services that run as root are usually stored in the keytab file
/etc/krb5.keytab. N.B.: This service key is the equivalent
of the service's password, and must be kept secure. Data which is meant
to be read only by the service is encrypted using this key.

2.7 The User/Kerberos Interaction

Suppose that you walk up to a host intending to login to it, and then
‘rlogin’ to the machine ‘laughter’. Here's what happens:

You login to the workstation and use the ‘kinit’ command to get a
ticket-granting ticket. This command prompts you for your Kerberos
password. (On systems running the Kerberos V5 ‘login’ program,
this may be done as part of the login process, not requiring the user to
run a separate program.)

If this entry exists, the Kerberos server creates and returns a
ticket-granting ticket and the key which allows you to use it, encrypted
by your password. If ‘kinit’ can decrypt the Kerberos reply using
the password you provide, it stores this ticket in a credentials cache
on your local machine for later use. The name of the credentials cache
can be specified in the ‘KRB5CCNAME’ environment variable. If this
variable is not set, the name of the file will be
/tmp/krb5cc_<uid>, where <uid> is your UNIX user-id, represented
in decimal format.

Now you use the ‘rlogin’ client to access the machine
‘laughter’.

host% rlogin laughter

The ‘rlogin’ client checks your ticket file to see if you have a
ticket for the ‘host’ service for ‘laughter’. You don't, so
‘rlogin’ uses the credential cache's ticket-granting ticket to make
a request to the master server's ticket-granting service.

This ticket-granting service receives the request for a ticket for
‘host/laughter.mit.edu’, and looks in the master
database for an entry for ‘host/laughter.mit.edu’.
If the entry exists, the ticket-granting service issues you a ticket for
that service. That ticket is also cached in your credentials cache.

The ‘rlogin’ client now sends that ticket to the ‘laughter’
‘klogind’ service program. The service program checks the ticket
by using its own service key. If the ticket is valid, it now knows your
identity. If you are allowed to login to ‘laughter’ (because your
username matches one in /etc/passwd, or your Kerberos principal is in
the appropriate .k5login file), klogind will let you
login.

2.8 Definitions

an entity that can obtain a ticket. This entity is usually either a
user or a host.

host

a computer that can be accessed over a network.

Kerberos

in Greek mythology, the three-headed dog that guards the entrance to the
underworld. In the computing world, Kerberos is a network security
package that was developed at MIT.

KDC

Key Distribution Center. A machine that issues Kerberos tickets.

keytab

a key table file containing one or more keys. A host or service
uses a keytab file in much the same way as a user uses his/her
password.

principal

a string that names a specific entity to which a set of credentials may
be assigned. It can have an arbitrary number of components, but
generally has three:

primary

the first part of a Kerberos principal. In the case of a user, it
is the username. In the case of a service, it is the name of the
service.

instance

the second part of a Kerberos principal. It gives information that
qualifies the primary. The instance may be null. In the case of a
user, the instance is often used to describe the intended use of the
corresponding credentials. In the case of a host, the instance is the
fully qualified hostname.

realm

the logical network served by a single Kerberos database and a set of
Key Distribution Centers. By convention, realm names are generally all
uppercase letters, to differentiate the realm from the internet domain.

The typical format of a typical Kerberos principal is
primary/instance@REALM.

service

any program or computer you access over a network. Examples of services
include “host” (a host, e.g., when you use telnet and
rsh), “ftp” (FTP), “krbtgt” (authentication;
cf. ticket-granting ticket), and “pop” (email).

ticket

a temporary set of electronic credentials that verify the identity of a
client for a particular service.

TGT

Ticket-Granting Ticket. A special Kerberos ticket that permits the
client to obtain additional Kerberos tickets within the same Kerberos
realm.

3 Configuration Files

3.1 Supported Encryption Types

Any tag in the configuration files which requires a list of encryption
types can be set to some combination of the following strings.
Encryption types marked as “weak” are available for compatibility
but not recommended for use.

des-cbc-crc

DES cbc mode with CRC-32 (weak)

des-cbc-md4

DES cbc mode with RSA-MD4 (weak)

des-cbc-md5

DES cbc mode with RSA-MD5 (weak)

des-cbc-raw

DES cbc mode raw (weak)

des3-cbc-raw

Triple DES cbc mode raw (weak)

des3-cbc-sha1

des3-hmac-sha1

des3-cbc-sha1-kd

Triple DES cbc mode with HMAC/sha1

des-hmac-sha1

DES with HMAC/sha1 (weak)

aes256-cts-hmac-sha1-96

aes256-cts

AES-256 CTS mode with 96-bit SHA-1 HMAC

aes128-cts-hmac-sha1-96

aes128-cts

AES-128 CTS mode with 96-bit SHA-1 HMAC

arcfour-hmac

rc4-hmac

arcfour-hmac-md5

RC4 with HMAC/MD5

arcfour-hmac-exp

rc4-hmac-exp

arcfour-hmac-md5-exp

Exportable RC4 with HMAC/MD5 (weak)

des

The DES family: des-cbc-crc, des-cbc-md5, and des-cbc-md4 (weak)

des3

The triple DES family: des3-cbc-sha1

aes

The AES family: aes256-cts-hmac-sha1-96 and aes128-cts-hmac-sha1-96

rc4

The RC4 family: arcfour-hmac

The string DEFAULT can be used to refer to the default set of types for
the variable in question. Types or families can be removed from the
current list by prefixing them with a minus sign (“-”). Types or
families can be prefixed with a plus sign (“+”) for symmetry; it has
the same meaning as just listing the type or family. For example,
“DEFAULT -des” would be the default set of encryption types with DES
types removed, and “des3 DEFAULT” would be the default set of
encryption types with triple DES types moved to the front.

While aes128-cts and aes256-cts are supported for all Kerberos
operations, they are not supported by older versions of our GSSAPI
implementation (krb5-1.3.1 and earlier).

By default, AES is enabled in this release. Sites wishing to use AES
encryption types on their KDCs need to be careful not to give GSSAPI
services AES keys if the servers have not been updated. If older
GSSAPI services are given AES keys, then services may fail when
clients supporting AES for GSSAPI are used. Sites may wish to use AES
for user keys and for the ticket granting ticket key, although doing
so requires specifying what encryption types are used as each
principal is created.

If all GSSAPI-based services have been updated before or with the KDC,
this is not an issue.

3.2 Salts

Your Kerberos key is derived from your password. To ensure that people
who happen to pick the same password do not have the same key, Kerberos
5 incorporates more information into the key using something called a
salt. The supported values for salts are as follows.

3.3 krb5.conf

The krb5.conf file contains Kerberos configuration information,
including the locations of KDCs and admin servers for the Kerberos
realms of interest, defaults for the current realm and for Kerberos
applications, and mappings of hostnames onto Kerberos realms. Normally,
you should install your krb5.conf file in the directory
/etc. You can override the default location by setting the
environment variable ‘KRB5_CONFIG’.

The krb5.conf file is set up in the style of a Windows INI file.
Sections are headed by the section name, in square brackets. Each
section may contain zero or more relations, of the form:

foo = bar

or

fubar = {
foo = bar
baz = quux
}

Placing a `*' at the end of a line indicates that this is the
final value for the tag. This means that neither the remainder
of this configuration file nor any other configuration file will be
checked for any other values for this tag.

For example, if you have the following lines:

foo = bar*
foo = baz

then the second value of foo (baz) would never be read.

The krb5.conf file can include other files using either of the
following directives at the beginning of a line:

include FILENAME
includedir DIRNAME

FILENAME or DIRNAME should be an absolute path. The named
file or directory must exist and be readable. Including a directory
includes all files within the directory whose names consist solely of
alphanumeric characters, dashes, or underscores. Included profile files
are syntactically independent of their parents, so each included file
must begin with a section header.

The krb5.conf file may contain any or all of the following
sections:

libdefaults

Contains default values used by the Kerberos V5 library.

login

Contains default values used by the Kerberos V5 login program.

appdefaults

Contains default values that can be used by Kerberos V5 applications.

realms

Contains subsections keyed by Kerberos realm names. Each subsection
describes realm-specific information, including where to find the
Kerberos servers for that realm.

domain_realm

Contains relations which map domain names and subdomains onto Kerberos
realm names. This is used by programs to determine what realm a host
should be in, given its fully qualified domain name.

logging

Contains relations which determine how Kerberos programs are to perform
logging.

capaths

Contains the authentication paths used with direct (nonhierarchical)
cross-realm authentication. Entries in this section are used by the
client to determine the intermediate realms which may be used in
cross-realm authentication. It is also used by the end-service when
checking the transited field for trusted intermediate realms.

plugins

Contains tags to register dynamic plugin modules and to turn modules on
and off.

3.3.1 [libdefaults]

This relation specifies the default keytab name to be used by
application servers such as telnetd and rlogind. The default is
/etc/krb5.keytab.

default_realm

Identifies the default Kerberos realm for the client. Set its value to
your Kerberos realm. If this is not specified and the TXT record
lookup is enabled (see Using DNS), then that information will be
used to determine the default realm. If this tag is not set in this
configuration file and there is no DNS information found, then an error
will be returned.

default_tgs_enctypes

Identifies the supported list of session key encryption types that
should be returned by the KDC. The list may be delimited with commas
or whitespace. Kerberos supports many different encryption types, and
support for more is planned in the future. (see Supported Encryption Types for a list of the accepted values for this tag). The default
value is aes256-cts-hmac-sha1-96 aes128-cts-hmac-sha1-96 des3-cbc-sha1 arcfour-hmac-md5 des-cbc-crc des-cbc-md5 des-cbc-md4.

default_tkt_enctypes

Identifies the supported list of session key encryption types that
should be requested by the client. The format is the same as for
default_tgs_enctypes. The default value for this tag is
aes256-cts-hmac-sha1-96 aes128-cts-hmac-sha1-96 des3-cbc-sha1 arcfour-hmac-md5 des-cbc-crc des-cbc-md5 des-cbc-md4.

permitted_enctypes

Identifies all encryption types that are permitted for use in session
key encryption. The default value for this tag is
aes256-cts-hmac-sha1-96 aes128-cts-hmac-sha1-96 des3-cbc-sha1 arcfour-hmac-md5 des-cbc-crc des-cbc-md5 des-cbc-md4.

allow_weak_crypto

If this is set to 0 (for false), then weak encryption types will be
filtered out of the previous three lists (as noted in Supported Encryption Types). The default value for this tag is false, which
may cause authentication failures in existing Kerberos infrastructures
that do not support strong crypto. Users in affected environments
should set this tag to true until their infrastructure adopts stronger
ciphers.

clockskew

Sets the maximum allowable amount of clockskew in seconds that the
library will tolerate before assuming that a Kerberos message is
invalid. The default value is 300 seconds, or five minutes.

ignore_acceptor_hostname

When accepting GSSAPI or krb5 security contexts for host-based service
principals, ignore any hostname passed by the calling application and
allow any service principal present in the keytab which matches the
service name and realm name (if given). This option can improve
the administrative flexibility of server applications multi-homed hosts,
but can compromise the security of virtual hosting environments. The
default value is false.

k5login_authoritative

If the value of this relation is true (the default), principals must
be listed in a local user's k5login file to be granted login access,
if a k5login file exists. If the value of this relation is false, a
principal may still be granted login access through other mechanisms
even if a k5login file exists but does not list the principal.

k5login_directory

If set, the library will look for a local user's k5login file within the
named directory, with a filename corresponding to the local username.
If not set, the library will look for k5login files in the user's home
directory, with the filename .k5login. For security reasons,
k5login files must be owned by the local user or by root.

kdc_timesync

If this is set to 1 (for true), then client machines will compute the
difference between their time and the time returned by the KDC in the
timestamps in the tickets and use this value to correct for an
inaccurate system clock. This corrective factor is only used by the
Kerberos library. The default is 1.

kdc_req_checksum_type

ap_req_checksum_type

safe_checksum_type

An integer which specifies the type of checksum to use. Used for
compatability with DCE security servers which do not support the
default RSA MD5 used by this version of Kerberos.
The
kdc_req_checksum_type is only used for DES keys. The ap_req_checksum_type defaults to the preferred checksum for the encryption type being used if unset. If set, then the selected checksum is used regardless of the type of key being used. The possible values and their meanings are as follows.

1

CRC32

2

RSA MD4

3

RSA MD4 DES

4

DES CBC

7

RSA MD5

8

RSA MD5 DES

9

NIST SHA

12

HMAC SHA1 DES3

-138

Microsoft MD5 HMAC checksum type

preferred_preauth_types

This allows you to set the preferred preauthentication types which the
client will attempt before others which may be advertised by a KDC. The
default value for this setting is "17, 16, 15, 14", which forces libkrb5
to attempt to use PKINIT if it is supported.

ccache_type

Use this parameter on systems which are DCE clients, to specify the
type of cache to be created by kinit, or when forwarded tickets are
received. DCE and Kerberos can share the cache, but some versions of
DCE do not support the default cache as created by this version of
Kerberos. Use a value of 1 on DCE 1.0.3a systems, and a value of 2 on
DCE 1.1 systems. The default value is 4.

dns_lookup_kdc

Indicate whether DNS SRV records should be used to locate the KDCs and
other servers for a realm, if they are not listed in the information for
the realm. (Note that the ‘admin_server’ entry must be in the
file, because the DNS implementation for it is incomplete.)

Enabling this option does open up a type of denial-of-service attack, if
someone spoofs the DNS records and redirects you to another server.
However, it's no worse than a denial of service, because that fake KDC
will be unable to decode anything you send it (besides the initial
ticket request, which has no encrypted data), and anything the fake KDC
sends will not be trusted without verification using some secret that it
won't know.

If this option is not specified but ‘dns_fallback’ is, that value
will be used instead. If neither option is specified, the behavior
depends on configure-time options; if none were given, the default is to
enable this option. If the DNS support is not compiled in, this entry
has no effect.

dns_lookup_realm

Indicate whether DNS TXT records should be used to determine the
Kerberos realm of a host.

Enabling this option may permit a redirection attack, where spoofed DNS
replies persuade a client to authenticate to the wrong realm, when
talking to the wrong host (either by spoofing yet more DNS records or by
intercepting the net traffic). Depending on how the client software
manages hostnames, however, it could already be vulnerable to such
attacks. We are looking at possible ways to minimize or eliminate this
exposure. For now, we encourage more adventurous sites to try using
Secure DNS.

If this option is not specified but ‘dns_fallback’ is, that value
will be used instead. If neither option is specified, the behavior
depends on configure-time options; if none were given, the default is to
disable this option. If the DNS support is not compiled in, this entry
has no effect.

dns_fallback

General flag controlling the use of DNS for Kerberos information. If
both of the preceding options are specified, this option has no effect.

realm_try_domains

Indicate whether a host's domain components should be used to determine
the Kerberos realm of the host. The value of this variable is an
integer: -1 means not to search, 0 means to try the host's domain
itself, 1 means to also try the domain's immediate parent, and so forth.
The library's usual mechanism for locating Kerberos realms is used to
determine whether a domain is a valid realm–which may involve
consulting DNS if dns_lookup_kdc is set. The default is not to search
domain components.

extra_addresses

This allows a computer to use multiple local addresses, in order to
allow Kerberos to work in a network that uses NATs. The addresses
should be in a comma-separated list.

udp_preference_limit

When sending a message to the KDC, the library will try using TCP before
UDP if the size of the message is above udp_preference_list.
If the message is smaller than udp_preference_list, then UDP
will be tried before TCP. Regardless of the size, both protocols will
be tried if the first attempt fails.

verify_ap_req_nofail

If this flag is set, then an attempt to get initial credentials will
fail if the client machine does not have a keytab. The default for the
flag is not set.

ticket_lifetime

The value of this tag is the default lifetime for
initial tickets. The default value for the tag is
1 day.

renew_lifetime

The value of this tag is the default renewable lifetime for
initial tickets. The default value for the tag is
0.

noaddresses

Setting this flag causes the initial Kerberos ticket to be addressless.
The default for the flag is set.

forwardable

If this flag is set, initial tickets by default will be forwardable.
The default value for this flag is not set.

proxiable

If this flag is set, initial tickets by default will be proxiable.
The default value for this flag is not set.

rdns

If set to false, prevent the use of reverse DNS resolution when
translating hostnames into service principal names. Defaults to
true. Setting this flag to false is more secure, but may force
users to exclusively use fully qualified domain names when
authenticating to services.

3.3.2 [appdefaults]

Each tag in the [appdefaults] section names a Kerberos V5 application
or an option that is used by some Kerberos V5 application[s]. The
value of the tag defines the default behaviors for that application.

The above four ways of specifying the value of an option are shown
in order of decreasing precedence. In this example, if telnet is
running in the realm EXAMPLE.COM, it should, by default, have
option1 and option2 set to true. However, a telnet program in the realm
ATHENA.MIT.EDU should have option1 set to false and option2 set
to true. Any other programs in ATHENA.MIT.EDU should have option2
set to false by default. Any programs running in other realms should
have option2 set to true.

The list of specifiable options for each application may be found in
that application's man pages. The application defaults specified here
are overridden by those specified in the [realms] section.

3.3.4 [realms]

Each tag in the [realms] section of the file is the name of a Kerberos
realm. The value of the tag is a subsection with relations that define
the properties of that particular realm. For each realm, the following
tags may be specified in the realm's subsection:

kdc

The name or address of a host running a KDC for that realm. An optional
port number, separated from the hostname by a colon, may be included.
If the name or address contains colons (for example, if it is an IPv6
address), enclose it in square brackets to distinguish the colon from a
port separator. For your computer to be able to communicate with the
KDC for each realm, this tag must be given a value in each realm
subsection in the configuration file, or there must be DNS SRV records
specifying the KDCs (see Using DNS).

master_kdc

Identifies the master KDC(s). Currently, this tag is used in only one
case: If an attempt to get credentials fails because of an invalid
password, the client software will attempt to contact the master KDC,
in case the user's password has just been changed, and the updated
database has not been propagated to the slave servers yet.

database_module

This relation indicates the name of the configuration section under [dbmodules] for database specific parameters used by the loadable database library.

admin_server

Identifies the host where the administration server is running.
Typically, this is the master Kerberos server. This tag must be given
a value in order to communicate with the kadmin server for the realm.

default_domain

This tag is used for Kerberos 4 compatibility. Kerberos 4 does not
require the entire hostname of a server to be in its principal like
Kerberos 5 does. This tag provides the domain name needed to produce a
full hostname when translating V4 principal names into V5 principal
names. All servers in this realm are assumed to be in the domain given
as the value of this tag

v4_instance_convert

This subsection allows the administrator to configure exceptions to the
default_domain mapping rule. It contains V4 instances (the tag name)
which should be translated to some specific hostname (the tag value) as
the second component in a Kerberos V5 principal name.

v4_realm

This relation is used by the krb524 library routines when converting a
V5 principal name to a V4 principal name. It is used when the V4 realm
name and the V5 realm name are not the same, but still share the same
principal names and passwords. The tag value is the Kerberos V4 realm
name.

auth_to_local_names

This subsection allows you to set explicit mappings from principal
names to local user names. The tag is the mapping name, and the value
is the corresponding local user name.

auth_to_local

This tag allows you to set a general rule for mapping principal names
to local user names. It will be used if there is not an explicit
mapping for the principal name that is being translated. The possible
values are:

DB:filename

The principal will be looked up in the database filename. Support
for this is not currently compiled in by default.

RULE:exp

The local name will be formulated from exp.

The format for exp is
[n:string](regexp)s/pattern/replacement/g.
The integer n indicates how many components the target principal
should have. If this matches, then a string will be formed from
string, substituting the realm of the principal for $0 and
the n'th component of the principal for $n (e.g. if the
principal was johndoe/admin then [2:$2$1foo] would result in
the string "adminjohndoefoo"). If this string matches
regexp, then the s//[g] substitution command will be run over
the string. The optional g will cause the substitution to be global
over the string, instead of replacing only the first match in the
string.

DEFAULT

The principal name will be used as the local user name. If the
principal has more than one component or is not in the default realm,
this rule is not applicable and the conversion will fail.

would result in any principal without root or admin as
the second component to be translated with the default rule. A
principal with a second component of admin will become its first
component. root will be used as the local name for any
principal with a second component of root. The exception to
these two rules are any principals johndoe/*, which will
always get the local name guest.

3.3.5 [domain_realm]

The [domain_realm] section provides a translation from a domain name or
hostname to a Kerberos realm name. The tag name can be a host name, or
a domain name, where domain names are indicated by a prefix of a period
(‘.’). The value of the relation is the Kerberos realm name for
that particular host or domain. Host names and domain names should be
in lower case.

If no translation entry applies, the host's realm is considered to be
the hostname's domain portion converted to upper case. For example, the
following [domain_realm] section:

maps crash.mit.edu into the TEST.ATHENA.MIT.EDU
realm. All other hosts in the mit.edu domain will map by
default to the ATHENA.MIT.EDU realm, and all hosts in the
example.com domain will map by default into the
EXAMPLE.COM realm. Note the entries for the hosts
mit.edu and example.com. Without these entries,
these hosts would be mapped into the Kerberos realms ‘EDU’ and
‘ORG’, respectively.

3.3.6 [logging]

The [logging] section indicates how a particular entity is to perform
its logging. The relations in this section assign one or more values to
the entity name. Currently, the following entities are used:

kdc

These entries specify how the KDC is to perform its logging.

admin_server

These entries specify how the administrative server
is to perform its logging.

default

These entries specify how to perform logging in the
absence of explicit specifications otherwise.

Values are of the following forms:

FILE=<filename>

FILE:<filename>

This value causes the entity's logging messages to go to the specified
file. If the ‘=’ form is used, the file is overwritten. If the
‘:’ form is used, the file is appended to.

STDERR

This value causes the entity's logging messages to go to its standard
error stream.

CONSOLE

This value causes the entity's logging messages to go to the console, if
the system supports it.

DEVICE=<devicename>

This causes the entity's logging messages to go to the specified device.

SYSLOG[:<severity>[:<facility>]]

This causes the entity's logging messages to go to the system log.

The severity argument specifies the default severity of system log
messages. This may be any of the following severities supported by the
syslog(3) call, minus the LOG_ prefix: LOG_EMERG, LOG_ALERT,
LOG_CRIT, LOG_ERR, LOG_WARNING, LOG_NOTICE, LOG_INFO, and LOG_DEBUG.
For example, a value of ‘CRIT’ would specify LOG_CRIT severity.

The facility argument specifies the facility under which the messages
are logged. This may be any of the following facilities supported by
the syslog(3) call minus the LOG_ prefix: LOG_KERN, LOG_USER, LOG_MAIL,
LOG_DAEMON, LOG_AUTH, LOG_LPR, LOG_NEWS, LOG_UUCP, LOG_CRON, and
LOG_LOCAL0 through LOG_LOCAL7.

If no severity is specified, the default is ERR. If no facility is
specified, the default is AUTH.

In the following example, the logging messages from the KDC will go to
the console and to the system log under the facility LOG_DAEMON with
default severity of LOG_INFO; and the logging messages from the
administrative server will be appended to the file /var/adm/kadmin.log
and sent to the device /dev/tty04.

3.3.7 [capaths]

In order to perform direct (non-hierarchical) cross-realm
authentication, a database is needed to construct the authentication
paths between the realms. This section defines that database.

A client will use this section to find the authentication path between
its realm and the realm of the server. The server will use this section
to verify the authentication path used by the client, by checking the
transited field of the received ticket.

There is a tag for each participating realm, and each tag has subtags
for each of the realms. The value of the subtags is an intermediate
realm which may participate in the cross-realm authentication. The
subtags may be repeated if there is more then one intermediate realm. A
value of "." means that the two realms share keys directly, and no
intermediate realms should be allowed to participate.

There are n**2 possible entries in this table, but only those entries
which will be needed on the client or the server need to be present.
The client needs a tag for its local realm, with subtags for all the
realms of servers it will need to authenticate with. A server needs a
tag for each realm of the clients it will serve.

For example, ANL.GOV, PNL.GOV, and NERSC.GOV all wish to use the ES.NET
realm as an intermediate realm. ANL has a sub realm of TEST.ANL.GOV
which will authenticate with NERSC.GOV but not PNL.GOV. The [capaths]
section for ANL.GOV systems would look like this:

In the above examples, the ordering is not important, except when the
same subtag name is used more then once. The client will use this to
determine the path. (It is not important to the server, since the
transited field is not sorted.)

This feature is not currently supported by DCE. DCE security servers
can be used with Kerberized clients and servers, but versions prior to
DCE 1.1 did not fill in the transited field, and should be used with
caution.

3.3.8 [dbdefaults]

The [dbdefaults] section provides default values for the database specific parameters. It can also specify the configuration section under [dbmodules] section for database specific parameters used by the database library.(see dbmodules).

The following tags are used in this section:

database_module

This relation indicates the name of the configuration section under the [dbmodules] for database specific parameters used by the loadable database library.

ldap_kerberos_container_dn

This LDAP specific tag indicates the DN of the container object where the realm objects will be located. This value is used if the container object is not mentioned in the configuration section under [dbmodules].

ldap_kdc_dn

This LDAP specific tag indicates the default bind DN for the KDC server. The KDC server does a login to the directory as this object. This object should have the rights to read the Kerberos data in the LDAP database. This value is used if the bind DN for the KDC is not mentioned in the configuration section under [dbmodules].

ldap_kadmind_dn

This LDAP specific tag indicates the default bind DN for the Administration server. The administration server does a login to the directory as this object. This object should have the rights to read and write the Kerberos data in the LDAP database. This value is used if the bind DN for the Administration server is not mentioned in the configuration section under [dbmodules].

ldap_service_password_file

This LDAP specific tag indicates the file containing the stashed passwords (created by kdb5_ldap_util stashsrvpw) for the objects used by the Kerberos servers to bind to the LDAP server. This file must be kept secure. This value is used if no service password file is mentioned in the configuration section under [dbmodules].

ldap_servers

This LDAP specific tag indicates the list of LDAP servers that the Kerberos servers can connect to. The list of LDAP servers is whitespace-separated. The LDAP server is specified by a LDAP URI. This value is used if no LDAP servers are mentioned in the configuration section under [dbmodules]. It is recommended to use the ldapi:// or ldaps:// interface and not to use ldap:// interface.

ldap_conns_per_server

This LDAP specific tag indicates the number of connections to be maintained per LDAP server. This value is used if the number of connections per LDAP server are not mentioned in the configuration section under [dbmodules]. The default value is 5.

3.3.9 [dbmodules]

Contains database specific parameters used by the database library. Each tag in the [dbmodules] section of the file names a configuration section for database specific parameters that can be referred to by a realm. The value of the tag is a subsection where the relations in that subsection define the database specific parameters.

For each section, the following tags may be specified in the subsection:

db_library

This tag indicates the name of the loadable database library. The value should be ‘db2’ for DB2 database and ‘kldap’ for LDAP database.

database_name

This DB2-specific tag indicates the location of the database in the
filesystem. The default is /usr/local/var/krb5kdc/principal.

disable_last_success

If set to true, suppresses KDC updates to the “Last successful
authentication” field of principal entries requiring preauthentication.
Setting this flag may improve performance. (Principal entries which do
not require preauthentication never update the “Last successful
authentication” field.)

disable_lockout

If set to true, suppresses KDC updates to the “Last failed
authentication” and “Failed password attempts” fields of principal
entries requiring preauthentication. Setting this flag may improve
performance, but also disables account lockout.

ldap_kerberos_container_dn

This LDAP specific tag indicates the DN of the container object where the realm objects will be located.

ldap_kdc_dn

This LDAP specific tag indicates the default bind DN for the KDC server. The KDC server does a login to the directory as this object. This object should have the rights to read the Kerberos data in the LDAP database.

ldap_kadmind_dn

This LDAP specific tag indicates the default bind DN for the Administration server. The administration server does a login to the directory as this object. This object should have the rights to read and write the Kerberos data in the LDAP database.

ldap_service_password_file

This LDAP specific tag indicates the file containing the stashed passwords (created by kdb5_ldap_util stashsrvpw) for the objects used by the Kerberos servers to bind to the LDAP server. This file must be kept secure.

ldap_servers

This LDAP specific tag indicates the list of LDAP servers that the Kerberos servers can connect to. The list of LDAP servers is whitespace-separated. The LDAP server is specified by a LDAP URI. It is recommended to use ldapi:// or ldaps:// interface to connect to the LDAP server.

ldap_conns_per_server

This LDAP specific tags indicates the number of connections to be maintained per LDAP server.

3.3.10 Plugins

Tags in the [plugins] section can be used to register dynamic plugin
modules and to turn modules on and off. Not every krb5 pluggable
interface uses the [plugins] section; the ones that do are documented
here.

Each pluggable interface corresponds to a subsection of [plugins].
All subsections support the same tags:

module

This tag may have multiple values. Each value is a string of the form
"modulename:pathname", which causes the shared object located at
pathname to be registered as a dynamic module named modulename for the
pluggable interface. If pathname is not an absolute path, it will be
treated as relative to the "krb5/plugins" subdirectory of the krb5
library directory.

enable_only

This tag may have multiple values. If there are values for this tag,
then only the named modules will be enabled for the pluggable
interface.

disable

This tag may have multiple values. If there are values for this tag,
then the named modules will be disabled for the pluggable interface.

The following subsections are currently supported within the [plugins]
section:

3.3.10.1 pwqual interface

The pwqual subsection controls modules for the password quality
interface, which is used to reject weak passwords when passwords are
changed. In addition to any registered dynamic modules, the following
built-in modules exist (and may be disabled with the disable tag):

dict

Checks against the realm dictionary file

empty

Rejects empty passwords

hesiod

Checks against user information stored in Hesiod (only if Kerberos was
built with Hesiod support)

3.3.10.2 kadm5_hook interface

The kadm5_hook interface provides plugins with information on
principal creation, modification, password changes and deletion. This
interface can be used to write a plugin to synchronize MIT Kerberos
with another database such as Active Directory. No plugins are built
in for this interface.

3.3.11 pkinit options

The following are pkinit-specific options.
Note that these values may be specified in [libdefaults]
as global defaults,
or within a realm-specific subsection of [libdefaults],
or may be specified as realm-specific values in the
[realms] section.
Also note that a realm-specific value over-rides, does not add to,
a generic [libdefaults] specification.
The search order is:

3.3.11.1 Specifying pkinit identity information

The syntax for specifying Public Key identity, trust, and revocation
information for pkinit is as follows:

FILE:file-name[,key-file-name]

This option has context-specific behavior.

pkinit_identity

pkinit_identities

file-name specifies the name of a PEM-format file
containing the user's certificate. If key-file-name is
not specified, the user's private key is expected to be
in file-name as well. Otherwise, key-file-name
is the name of the file containing the private key.

pkinit_anchors

pkinit_pool

file-name is assumed to be the name of an OpenSSL-style
ca-bundle file.

DIR:directory-name

This option has context-specific behavior.

pkinit_identity

pkinit_identities

directory-name specifies a directory with files named
*.crt and *.key, where the first part of the
file name is the same for matching pairs of certificate and
private key files. When a file with a name ending with .crt
is found, a matching file ending with .key is assumed
to contain the private key. If no such file is found, then
the certificate in the .crt is not used.

pkinit_anchors

pkinit_pool

directory-name is assumed to be an OpenSSL-style hashed CA directory
where each CA cert is stored in a file named hash-of-ca-cert.#.
This infrastructure is encouraged, but all files in the directory
will be examined and if they contain certificates (in PEM format),
they will be used.

pkinit_revoke

directory-name is assumed to be an OpenSSL-style hashed CA directory
where each revocation list is stored in a file named hash-of-ca-cert.r#.
This infrastructure is encouraged, but all files in the directory
will be examined and if they contain a revocation list (in PEM format),
they will be used.

PKCS12:pkcs12-file-name

pkcs12-file-name is the name of a PKCS #12 format file, containing
the user's certificate and private key.

All keyword/values are optional.
module-name specifies the location of a library implementing
PKCS #11. If a value is encountered with no keyword, it
is assumed to be the module-name. If no module-name is
specified, the default is opensc-pkcs11.so.
slotid= and/or token= may be specified to force the use of a
particular smard card reader or token if there is more than one
available.
certid= and/or certlabel= may be specified to force the selection
of a particular certificate on the device. See the pkinit_cert_match
configuration option for more ways to select a particular certificate to
use for pkinit.

ENV:environment-variable-name

environment-variable-name specifies the name of an environment
variable which has been set to a value conforming to one of the
previous values. For example, ENV:X509_PROXY, where environment
variable X509_PROXY has been set to FILE:/tmp/my_proxy.pem.

3.3.11.2 pkinit krb5.conf options

pkinit_identities

Specifies the location(s) to be used to find the user's X.509 identity
information. This option may be specified multiple times.
Each value is attempted in order until identity information is found
and authentication is attempted. Note that these values are not
used if the user specifies X509_user_identity on the command line.

pkinit_anchors

Specifies the location of trusted anchor (root) certificates which
the client trusts to sign KDC certificates. This option may be
specified multiple times. These values from the config file are
not used if the user specifies X509_anchors on the command line.

pkinit_pool

Specifies the location of intermediate certificates which may be
used by the client to complete the trust chain between a KDC
certificate and a trusted anchor. This option may be specified
multiple times.

pkinit_revoke

Specifies the location of Certificate Revocation List (CRL) information
to be used by the client when verifying the validity of the KDC
certificate presented. This option may be specified multiple times.

pkinit_require_crl_checking

The default certificate verification process will always check
the available revocation information to see if a certificate has
been revoked. If a match is found for the certificate in a CRL,
verification fails. If the certificate being verified is not listed
in a CRL, or there is no CRL present for its issuing CA,
and pkinit_require_crl_checking is false,
then verification succeeds.

However, if pkinit_require_crl_checking is true and
there is no CRL information available for the issuing CA,
then verification fails.

pkinit_require_crl_checking should be set to true
if the policy is such that up-to-date CRLs must be present for
every CA.

pkinit_dh_min_bits

Specifies the size of the Diffie-Hellman key the client will
attempt to use. The acceptable values are currently 1024, 2048,
and 4096. The default is 2048.

pkinit_win2k

This flag specifies whether the target realm is assumed
to support only the old, pre-RFC version of the protocol.
The default is false.

pkinit_win2k_require_binding

If this flag is set to true, it expects that the target
KDC is patched to return a reply with a checksum rather than a
nonce. The default is false.

pkinit_eku_checking

This option specifies what Extended Key Usage value the KDC certificate
presented to the client must contain.
(Note that if the KDC certificate has the pkinit
SubjectAlternativeName encoded as the Kerberos TGS name, EKU checking
is not necessary since the issuing CA has certified this as a KDC
certificate.)
The values recognized in the krb5.conf file are:

kpKDC

This is the default value and specifies that the KDC must have the
id-pkinit-KPKdc EKU as defined in RFC4556.

kpServerAuth

If kpServerAuth is specified, a KDC certificate with the
id-kp-serverAuth EKU as used by Microsoft will be accepted.

none

If none is specified, then the KDC certificate will not be
checked to verify it has an acceptable EKU. The use of this option
is not recommended.

pkinit_kdc_hostname

The presense of this option indicates that the client is willing to
accept a KDC certificate with a dNSName SAN (Subject Alternative Name)
rather than requiring the id-pkinit-san as defined in RFC4556. This
option may be specified multiple times. Its value should contain
the acceptable hostname for the KDC (as contained in its certificate).

pkinit_cert_match

Specifies matching rules that the client certificate must match before
it is used to attempt pkinit authentication. If a user has multiple
certificates available (on a smart card, or via other media), there
must be exactly one certificate chosen before attempting pkinit
authentication. This option may be specified multiple times. All the
available certificates are checked against each rule in order until
there is a match of exactly one certificate.

The Subject and Issuer comparison strings are the RFC2253 string
representations from the certificate Subject DN and Issuer DN values.

The syntax of the matching rules is:

[relation-operator]component-rule...

where

relation-operator

can be either &&, meaning all component rules must match,
or ||, meaning only one component rule must match.
The default is && if not specified.

component-rule

can be one of the following. Note that there is no punctuation
or whitespace between component rules.

<SUBJECT>regular-expression

<ISSUER>regular-expression

<SAN>regular-expression

<EKU>extended-key-usage-list

where extended-key-usage-list is a comma-separated list of
required Extended Key Usage values. All values in the list must
be present in the certificate.

pkinitmsScLoginclientAuthemailProtection

<KU>key-usage-list

where key-usage-list is a comma-separated list of required
Key Usage values. All values in the list must be present in
the certificate.

3.4 kdc.conf

The kdc.conf file contains KDC configuration information,
including defaults used when issuing Kerberos tickets. Normally, you
should install your kdc.conf file in the directory
/usr/local/var/krb5kdc. You can override the default
location by setting the environment variable ‘KRB5_KDC_PROFILE’.

The kdc.conf file is set up in the same format as the
krb5.conf file. (See krb5.conf.) The kdc.conf file
may contain any or all of the following three sections:

kdcdefaults

Contains default values for overall behavior of the KDC.

realms

Contains subsections keyed by Kerberos realm names. Each subsection
describes realm-specific information, including where to find the
Kerberos servers for that realm.

logging

Contains relations which determine how Kerberos programs are to perform
logging.

3.4.1 [kdcdefaults]

The following relation is defined in the [kdcdefaults] section:

kdc_ports

This relation lists the ports on which the Kerberos server should
listen for UDP requests by default. This list is a comma separated
list of integers.
If this relation is not specified, the compiled-in default is
88,750, the first being the assigned Kerberos port
and the second which was used by Kerberos V4.

kdc_tcp_ports

This relation lists the ports on which the Kerberos server should
listen for TCP connections by default. This list is a comma separated
list of integers.
If this relation is not specified, the compiled-in default is not to
listen for TCP connections at all.

If you wish to change this (which we do not recommend, because the
current implementation has little protection against denial-of-service
attacks), the standard port number assigned for Kerberos TCP traffic
is port 88.

restrict_anonymous_to_tgt

This flag determines the default value of restrict_anonymous_to_tgt for
realms. The default value is false.

3.4.2 [realms]

Each tag in the [realms] section of the file names a Kerberos realm.
The value of the tag is a subsection where the relations in that
subsection define KDC parameters for that particular realm.

For each realm, the following tags may be specified in the [realms]
subsection:

acl_file

(String.) Location of the access control list (acl) file that kadmin
uses to determine which principals are allowed which permissions on the
database. The default is /usr/local/var/krb5kdc/kadm5.acl.

admin_keytab

(String.) Location of the keytab file that the legacy administration
daemons kadmind4 and v5passwdd use to authenticate to
the database. The default is /usr/local/var/krb5kdc/kadm5.keytab.

default_principal_expiration

(Absolute time string.) Specifies the default expiration date of
principals created in this realm. The default value for this tag is
0.

default_principal_flags

(Flag string.) Specifies the default attributes of principals created
in this realm. The format for this string is a comma-separated list of
flags, with '+' before each flag that should be enabled and '-' before
each flag that should be disabled. The default is
postdateable, forwardable, tgt-based, renewable, proxiable, dup-skey, allow-tickets, and service enabled..

There are a number of possible flags:

postdateable

Enabling this flag allows the principal to obtain postdateable tickets.

forwardable

Enabling this flag allows the principal to obtain forwardable tickets.

tgt-based

Enabling this flag allows a principal to obtain tickets based on a
ticket-granting-ticket, rather than repeating the authentication
process that was used to obtain the TGT.

renewable

Enabling this flag allows the principal to obtain renewable tickets.

proxiable

Enabling this flag allows the principal to obtain proxy tickets.

dup-skey

Enabling this flag allows the principal to obtain a session key for
another user, permitting user-to-user authentication for this principal.

allow-tickets

Enabling this flag means that the KDC will issue tickets for this
principal. Disabling this flag essentially deactivates the principal
within this realm.

preauth

If this flag is enabled on a client principal, then that principal is
required to preauthenticate to the KDC before receiving any tickets.
On a service principal, enabling this flag means that service tickets
for this principal will only be issued to clients with a TGT that has
the preauthenticated ticket set.

hwauth

If this flag is enabled, then the principal is required to
preauthenticate using a hardware device before receiving any tickets.

pwchange

Enabling this flag forces a password change for this principal.

service

Enabling this flag allows the the KDC to issue service tickets for this
principal.

pwservice

If this flag is enabled, it marks this principal as a password change
service. This should only be used in special cases, for example, if a
user's password has expired, then the user has to get tickets for that
principal without going through the normal password authentication in
order to be able to change the password.

dict_file

(String.) Location of the dictionary file containing strings that are
not allowed as passwords. If none is specified or if there is no
policy assigned to the principal, no dictionary checks of passwords
will be performed.

kadmind_port

(Port number.) Specifies the port on which the kadmind daemon is to
listen for this realm. The assigned port for kadmind is
749.

kpasswd_port

(Port number.) Specifies the port on which the kpasswd daemon is to
listen for this realm. The default is 464.

key_stash_file

(String.) Specifies the location where the master key has been stored
(via kdb5_util stash). The default is
/usr/local/var/krb5kdc/.k5.REALM, where REALM is the
Kerberos realm.

kdc_ports

(String.) Specifies the list of ports that the KDC is to listen to
for UDP requests for this realm. By default, the value of kdc_ports
as specified in the [kdcdefaults] section is used.

kdc_tcp_ports

(String.) Specifies the list of ports that the KDC is to listen to
for TCP requests for this realm. By default, the value of
kdc_tcp_ports as specified in the [kdcdefaults] section is used.

master_key_name

(String.) Specifies the name of the principal associated with the
master key. The default is K/M.

master_key_type

(Key type string.) Specifies the master key's key type. The default
value for this is des3-cbc-sha1. For a list of all
possible values, see Supported Encryption Types.

max_life

(Delta time string.) Specifes the maximum time period for which a
ticket may be valid in this realm. The default value is
24 hours.

max_renewable_life

(Delta time string.) Specifies the maximum time period during which a
valid ticket may be renewed in this realm. The default value is
0.

supported_enctypes

List of key:salt strings. Specifies the default key/salt combinations of
principals for this realm. Any principals created through kadmin
will have keys of these types. The default value for this tag is
aes256-cts-hmac-sha1-96:normal aes128-cts-hmac-sha1-96:normal des3-cbc-sha1:normal arcfour-hmac-md5:normal. For lists of possible values, see
Supported Encryption Types and Salts.

reject_bad_transit

A boolean value (true, false). If set to true, the
KDC will check the list of transited realms for cross-realm tickets
against the transit path computed from the realm names and the
capaths section of its krb5.conf file; if the path in the
ticket to be issued contains any realms not in the computed path, the
ticket will not be issued, and an error will be returned to the client
instead. If this value is set to false, such tickets will be
issued anyways, and it will be left up to the application server to
validate the realm transit path.

If the disable-transited-check flag is set in the incoming
request, this check is not performed at all. Having the
reject_bad_transit option will cause such ticket requests to be
rejected always.

This transit path checking and config file option currently apply only
to TGS requests.

Earlier versions of the MIT release (before 1.2.3) had bugs in the
application server support such that the server-side checks may not be
performed correctly. We recommend turning this option on, unless you
know that all application servers in this realm have been updated to
fixed versions of the software, and for whatever reason, you don't want
the KDC to do the validation.

This is a per-realm option so that multiple-realm KDCs may control it
separately for each realm, in case (for example) one realm has had the
software on its application servers updated but another has not.

This option defaults to true.

restrict_anonymous_to_tgt

A boolean value (true, false). If set to true, the
KDC will reject ticket requests from anonymous principals to service
principals other than the realm's ticket-granting service. This option
allows anonymous PKINIT to be enabled for use as FAST armor tickets
without allowing anonymous authentication to services. By default, the
value of restrict_anonymous_to_tgt as specified in the [kdcdefaults]
section is used.

3.4.3 pkinit options

The following are pkinit-specific options.
Note that these values may be specified in [kdcdefaults]
as global defaults,
or within a realm-specific subsection of [realms].
Also note that a realm-specific value over-rides, does not add to,
a generic [kdcdefaults] specification.
The search order is:

3.4.3.1 pkinit kdc.conf options

Specifies the location of the KDC's X.509 identity information.
This option is required if pkinit is to be supported by the
KDC.

pkinit_anchors

Specifies the location of trusted anchor (root) certificates
which the KDC trusts to sign client certificates.
This option is required if pkinit is to be supported by the
KDC.
This option may be specified multiple times.

pkinit_pool

Specifies the location of intermediate certificates which may be
used by the KDC to complete the trust chain between a client's
certificate and a trusted anchor.
This option may be specified multiple times.

pkinit_revoke

Specifies the location of Certificate Revocation List (CRL)
information to be used by the KDC when verifying the validity
of client certificates.
This option may be specified multiple times.

pkinit_require_crl_checking

The default certificate verification process will always check
the available revocation information to see if a certificate has
been revoked. If a match is found for the certificate in a CRL,
verification fails. If the certificate being verified is not listed
in a CRL, or there is no CRL present for its issuing CA,
and pkinit_require_crl_checking is false,
then verification succeeds.

However, if pkinit_require_crl_checking is true and
there is no CRL information available for the issuing CA,
then verification fails.

pkinit_require_crl_checking should be set to true
if the policy is such that up-to-date CRLs must be present for
every CA.

pkinit_dh_min_bits

Specifies the minimum number of bits the KDC is willing to accept
for a client's Diffie-Hellman key. The default is 2048.

pkinit_allow_upn

Specifies that the KDC is willing to accept client certificates with
the Microsoft UserPrincipalName (UPN) Subject Alternative Name
(SAN). This means the KDC accepts the binding of the UPN in the
certificate to the Kerberos principal name.

The default is false.

Without this option, the KDC will only
accept certificates with the id-pkinit-san as defined in RFC4556.
There is currently no option to disable SAN checking in the KDC.

pkinit_eku_checking

This option specifies what Extended Key Usage (EKU) values the
KDC is willing to accept in client certificates.
The values recognized in the kdc.conf file are:

kpClientAuth

This is the default value and specifies that client certificates must
have the id-pkinit-KPClientAuth EKU as defined in RFC4556.

scLogin

If scLogin is specified, client certificates with the
Microsoft Smart Card Login EKU (id-ms-kp-sc-logon) will be accepted.

none

If none is specified, then client certificates will not be
checked to verify they have an acceptable EKU.
The use of this option is not recommended.

4 Using DNS

4.1 Mapping Hostnames onto Kerberos Realms

Mapping hostnames onto Kerberos realms is done in one of two ways.

The first mechanism, which has been in use for years in MIT-based
Kerberos distributions, works through a set of rules in
the krb5.conf configuration file. (See krb5.conf.) You can
specify mappings for an entire domain or subdomain, and/or on a
hostname-by-hostname basis. Since greater specificity takes precedence,
you would do this by specifying the mappings for a given domain or
subdomain and listing the exceptions.

The second mechanism works by looking up the information in special
TXT records in the Domain Name Service. This is currently not
used by default because security holes could result if the DNS TXT
records were spoofed. If this mechanism is enabled on the client,
it will try to look up a TXT record for the DNS name formed by
putting the prefix _kerberos in front of the hostname in question.
If that record is not found, it will try using _kerberos and the
host's domain name, then its parent domain, and so forth. So for the
hostname BOSTON.ENGINEERING.FOOBAR.COM, the names looked up would be:

The value of the first TXT record found is taken as the realm name.
(Obviously, this doesn't work all that well if a host and a subdomain
have the same name, and different realms. For example, if all the hosts
in the ENGINEERING.FOOBAR.COM domain are in the ENGINEERING.FOOBAR.COM
realm, but a host named ENGINEERING.FOOBAR.COM is for some reason in
another realm. In that case, you would set up TXT records for all
hosts, rather than relying on the fallback to the domain name.)

Even if you do not choose to use this mechanism within your site, you
may wish to set it up anyway, for use when interacting with other sites.

4.2 Hostnames for KDCs

MIT recommends that your KDCs have a predefined set of
CNAME records (DNS hostname aliases), such as kerberos
for the master KDC and
kerberos-1, kerberos-2, ... for the
slave KDCs. This way, if you need to swap a machine, you only need to
change a DNS entry, rather than having to change hostnames.

A new mechanism for locating KDCs of a realm through DNS has been added
to the MIT Kerberos V5 distribution. A relatively new
record type called SRV has been added to DNS. Looked up by a
service name and a domain name, these records indicate the hostname and
port number to contact for that service, optionally with weighting and
prioritization. (See RFC 2782 if you want more information. You can
follow the example below for straightforward cases.)

The use with Kerberos is fairly straightforward. The domain name used
in the SRV record name is the domain-style Kerberos realm name. (It is
possible to have Kerberos realm names that are not DNS-style names, but
we don't recommend it for Internet use, and our code does not support it
well.) Several different Kerberos-related service names are used:

_kerberos._udp

This is for contacting any KDC by UDP. This entry will be used the most
often. Normally you should list port 88 on each of your KDCs.

_kerberos._tcp

This is for contacting any KDC by TCP. The MIT KDC by default will not
listen on any TCP ports, so unless you've changed the configuration or
you're running another KDC implementation, you should leave this
unspecified. If you do enable TCP support, normally you should use
port 88.

_kerberos-master._udp

This entry should refer to those KDCs, if any, that will immediately see
password changes to the Kerberos database. This entry is used only in
one case, when the user is logging in and the password appears to be
incorrect; the master KDC is then contacted, and the same password used
to try to decrypt the response, in case the user's password had recently
been changed and the first KDC contacted hadn't been updated. Only if
that fails is an “incorrect password” error given.

If you have only one KDC, or for whatever reason there is no accessible
KDC that would get database changes faster than the others, you do not
need to define this entry.

_kerberos-adm._tcp

This should list port 749 on your master KDC.
Support for it is not complete at this time, but it will eventually be
used by the kadmin program and related utilities. For now, you
will also need the admin_server entry in krb5.conf.
(See krb5.conf.)

_kpasswd._udp

This should list port 464 on your master KDC.
It is used when a user changes her password.

Be aware, however, that the DNS SRV specification requires that the
hostnames listed be the canonical names, not aliases. So, for example,
you might include the following records in your (BIND-style) zone file:

As with the DNS-based mechanism for determining the Kerberos realm of a
host, we recommend distributing the information this way for use by
other sites that may want to interact with yours using Kerberos, even if
you don't immediately make use of it within your own site. If you
anticipate installing a very large number of machines on which it will
be hard to update the Kerberos configuration files, you may wish to do
all of your Kerberos service lookups via DNS and not put the information
(except for admin_server as noted above) in future versions of
your krb5.conf files at all. Eventually, we hope to phase out
the listing of server hostnames in the client-side configuration files;
making preparations now will make the transition easier in the future.

5 Administrating the Kerberos Database

Your Kerberos database contains all of your realm's Kerberos principals,
their passwords, and other administrative information about each
principal. For the most part, you will use the kdb5_util program
to manipulate the Kerberos database as a whole, and the kadmin
program to make changes to the entries in the database. (One notable
exception is that users will use the kpasswd program to change
their own passwords.) The kadmin program has its own
command-line interface, to which you type the database administrating
commands.

Kdb5_util provides a means to create, delete, load, or dump a
Kerberos database. It also includes a command to stash a copy of the
master database key in a file on a KDC, so that the KDC can authenticate
itself to the kadmind and krb5kdc daemons at boot time.

Kadmin provides for the maintenance of Kerberos principals, KADM5
policies, and service key tables (keytabs). It exists as both a
Kerberos client, kadmin, using Kerberos authentication and an
RPC, to operate securely from anywhere on the network, and as a local
client, kadmin.local, intended to run directly on the KDC without
Kerberos authentication. kadmin.local need not run on the kdc if
the database is LDAP. Other than the fact that the remote client uses
Kerberos to authenticate the person using it, the functionalities of the two
versions are identical. The local version is necessary to enable you to set up
enough of the database to be able to use the remote version.
It replaces the now obsolete kdb5_edit (except for
database dump and load, which are provided by kdb5_util).

The remote version authenticates to the KADM5 server using the service
principal kadmin/admin. If the credentials cache contains a
ticket for the kadmin/admin principal, and the ‘-c ccache’
option is specified, that ticket is used to authenticate to KADM5.
Otherwise, the ‘-p’ and ‘-k’ options are used to specify the
client Kerberos principal name used to authenticate. Once kadmin has
determined the principal name, it requests a kadmin/admin
Kerberos service ticket from the KDC, and uses that service ticket to
authenticate to KADM5.

5.1 Kadmin Options

You can invoke kadmin or kadmin.local with any of the
following options:

-r REALM

Use REALM as the default Kerberos realm for the database.

-p principal

Use the Kerberos principal principal to authenticate to Kerberos.
If this option is not given, kadmin will append admin to
either the primary principal name, the environment variable USER, or to
the username obtained from getpwuid, in order of preference.

-q query

Pass query directly to kadmin. This is useful for writing
scripts that pass specific queries to kadmin.

You can invoke kadmin with any of the following options:

-k [-t keytab]

Use the keytab keytab to decrypt the KDC response instead of
prompting for a password on the TTY. In this case, the principal will
be ‘host/hostname’. If -t is not used to specify a keytab,
then the default keytab will be used.

-c credentials cache

Use credentials_cache as the credentials cache. The credentials
cache should contain a service ticket for the kadmin/admin
service, which can be acquired with the kinit program. If this
option is not specified, kadmin requests a new service ticket
from the KDC, and stores it in its own temporary ccache.

-w password

Use password as the password instead of prompting for one on the
TTY. Note: placing the password for a Kerberos principal with
administration access into a shell script can be dangerous if
unauthorized users gain read access to the script.

-x db_args

Specifies the database specific arguments.

-x host=<hostname>

Specifies the LDAP server to connect to by a LDAP URI. It is recommend to use
ldapi:// or ldaps:// interface to connect to the LDAP server.

-x binddn=<bind_dn>

Specifies the Distinguished Name (DN) of the object used by the administration server to bind to the LDAP server. This object should have the read and write rights on the realm container, principal container and realm subtree.

-x bindpwd=<bind_password>

Specifies the password for the above mentioned binddn. It is recommended not to
use this option. Instead, the password can be stashed using the
stashsrvpw command of kdb5_ldap_util.

Note: This database specific argument is applicable only to kadmin.local
and the KADM5 server.

Note that if the date specification contains spaces, you must enclose it
in double quotes. Note also that you cannot use a number without a
unit. (I.e., “"60 seconds"” is correct, but “60” is incorrect.)
All keywords are case-insensitive. The following is a list of all of
the allowable keywords.

5.3.1.2 Retrieving a List of Principals

To generate a listing of principals, use the kadminlist_principals command, which requires the “list” privilege.
The syntax is:

list_principals [expression]

where expression is a shell-style glob expression that
can contain the characters ‘*’, ‘?’, ‘[’, and ‘]’.
All policy names matching the expression are displayed. The
list_principals command has the aliases listprincs,
get_principals, and getprincs. For example:

5.3.2 Privileges

Administrative privileges for the Kerberos database are stored in the
file kadm5.acl.

The format of the file is:

Kerberos_principal permissions [target_principal] [restrictions]

The Kerberos principal (and optional target principal) can include the
“*” wildcard, so if you want any principal with the instance
“admin” to have full permissions on the database, you could use the
principal “*/admin@REALM” where “REALM” is your Kerberos
realm. target_principal can also include backreferences to
Kerberos_principal, in which "*number" matches the
component number in the Kerberos_principal.

Note: a common use of an admin instance is so you can grant
separate permissions (such as administrator access to the Kerberos
database) to a separate Kerberos principal. For example, the user
joeadmin might have a principal for his administrative
use, called joeadmin/admin. This way,
joeadmin would obtain joeadmin/admin
tickets only when he actually needs to use those permissions.

The permissions are represented by single letters; UPPER-CASE letters
represent negative permissions. The permissions are:

a

allows the addition of principals or policies in the database.

A

disallows the addition of principals or policies in the database.

d

allows the deletion of principals or policies in the database.

D

disallows the deletion of principals or policies in the database.

m

allows the modification of principals or policies in the database.

M

disallows the modification of principals or policies in the database.

c

allows the changing of passwords for principals in the database.

C

disallows the changing of passwords for principals in the database.

i

allows inquiries to the database.

I

disallows inquiries to the database.

l

allows the listing of principals or policies in the database.

L

disallows the listing of principals or policies in the database.

s

allows the explicit setting of the key for a principal

S

disallows the explicit setting of the key for a principal

*

All privileges (admcil).

x

All privileges (admcil); identical to “*”.

The restrictions are a string of flags. Allowed restrictions are:

[+ -]flagname

flag is forced to indicated value. The permissible flags are the same
as the + and - flags for the kadmin addprinc and
modprinc commands.

-clearpolicy

policy is forced to clear

-policy pol

policy is forced to be pol

expire time

pwexpire time

maxlife time

maxrenewlife time

associated value will be forced to MIN(time, requested value)

The above flags act as restrictions on any add or modify operation
which is allowed due to that ACL line.

Here is an example of a kadm5.acl file. Note that order is
important; permissions are determined by the first matching entry.

In the above file, any principal in the
ATHENA.MIT.EDU realm with an admin instance has all
administrative privileges. The user joeadmin
has all permissions with his admin instance,
joeadmin/admin@ATHENA.MIT.EDU (matches the first
line). He has no permissions at all with his null instance,
joeadmin@ATHENA.MIT.EDU (matches the second line).
His root instance has inquire and list permissions with any
other principal that has the instance root. Any principal
in ATHENA.MIT.EDU can inquire, list, or change the password of
their admin instance, but not any other admin instance.
Any principal in the realm ATHENA.MIT.EDU (except for
joeadmin@ATHENA.MIT.EDU, as mentioned above) has
inquire privileges. Finally, any principal with an admin instance
in EXAMPLE.COM has all permissions, but any principal that they
create or modify will not be able to get postdateable tickets or tickets
with a life of longer than 9 hours.

5.3.3 Adding or Modifying Principals

To add a principal to the database, use the kadmin add_principal
command, which requires the “add” administrative privilege. This
function creates the new principal, prompting twice for a password, and,
if neither the -policy nor -clearpolicy options are specified and the
policy “default” exists, assigns it that policy. The syntax is:

kadmin: add_principal [options] principal

To modify attributes of a principal, use the kadmin
modify_principal command, which requires the “modify”
administrative privilege. The syntax is:

kadmin: modify_principal [options] principal

add_principal has the aliases addprinc and
ank2. modify_principal has the alias modprinc.

The add_principal and modify_principal commands take the
following switches:

Specifies the LDAP object that will contain the Kerberos principal being created.

-x linkdn=<dn>

Specifies the LDAP object to which the newly created Kerberos principal object will point to.

-x containerdn=<container_dn>

Specifies the container object under which the Kerberos principal is to be created.

-x tktpolicy=<policy>

Associates a ticket policy to the Kerberos principal. Specifying an empty string
value clears the ticket policy associated with the principal.
Note:
* dn and containerdn options are not valid while modifying the principal.
* containerdn and linkdn options cannot be specified with dn option.
* If dn or containerdn options are not specified while adding the principal, the principals are created
under the prinicipal container configured in the realm or the realm container.
* dn and containerdn should be within the subtrees or principal container configured in the realm.

-expire date

Sets the expiration date of the principal to date.

-pwexpire date

Sets the expiration date of the password to date.

-maxlife maxlife

Sets the maximum ticket life of the principal to maxlife.

-maxrenewlife maxrenewlife

Sets the maximum renewable life of tickets for the principal to
maxrenewlife.

-kvno number

Explicity sets the key version number to number. MIT
does not recommend doing this unless there is a specific reason.

-policy policy

Sets the policy used by this principal. (See Policies.) With
modify_principal, the current policy assigned to the principal is
set or changed. With add_principal, if this option is not
supplied, the -clearpolicy is not specified, and the policy “default”
exists, that policy is assigned. If a principal is created with no
policy, kadmin will print a warning message.

-clearpolicy

For modify_principal, removes the current policy from a
principal. For add_principal, suppresses the automatic
assignment of the policy “default”.

{-|+}allow_postdated

The “-allow_postdated” option prohibits this principal from obtaining
postdated tickets. “+allow_postdated” clears this flag. In effect,
“-allow_postdated” sets the KRB5_KDB_DISALLOW_POSTDATED flag on the
principal in the database.

{-|+}allow_forwardable

The “-allow_forwardable” option prohibits this principal from
obtaining forwardable tickets. “+allow_forwardable” clears this flag.
In effect, “-allow_forwardable” sets the KRB5_KDB_DISALLOW_FORWARDABLE
flag on the principal in the database.

{-|+}allow_renewable

The “-allow_renewable” option prohibits this principal from obtaining
renewable tickets. “+allow_renewable” clears this flag. In effect,
“-allow_renewable” sets the KRB5_KDB_DISALLOW_RENEWABLE flag on the
principal in the database.

{-|+}allow_proxiable

The “-allow_proxiable” option prohibits this principal from obtaining
proxiable tickets. “+allow_proxiable” clears this flag. In effect,
“-allow_proxiable” sets the KRB5_KDB_DISALLOW_PROXIABLE flag. on
the principal in the database.

{-|+}allow_dup_skey

The “-allow_dup_skey” option disables user-to-user authentication for
this principal by prohibiting this principal from obtaining a session
key for another user. “+allow_dup_skey” clears this flag. In effect,
“-allow_dup_skey” sets the KRB5_KDB_DISALLOW_DUP_SKEY flag on the
principal in the database.

{-|+}requires_preauth

The “+requires_preauth” option requires this principal to
preauthenticate before being allowed to kinit. -requires_preauth clears
this flag. In effect, +requires_preauth sets the
KRB5_KDB_REQUIRES_PRE_AUTH flag on the principal in the database.

{-|+}requires_hwauth

The “+requires_hwauth” flag requires the principal to preauthenticate
using a hardware device before being allowed to kinit.
“-requires_hwauth” clears this flag. In effect, “+requires_hwauth”
sets the KRB5_KDB_REQUIRES_HW_AUTH flag on the principal in the
database.

{-|+}allow_svr

The “-allow_svr” flag prohibits the issuance of service tickets for
this principal. “+allow_svr” clears this flag. In effect,
“-allow_svr” sets the KRB5_KDB_DISALLOW_SVR flag on the principal
in the database.

{-|+}allow_tgs_req

The “-allow_tgs_req” option specifies that a Ticket-Granting Service
(TGS) request for a service ticket for this principal is not permitted.
You will probably never need to use this option. “+allow_tgs_req”
clears this flag. The default is “+allow_tgs_req”. In effect,
“-allow_tgs_req” sets the KRB5_KDB_DISALLOW_TGT_BASED flag on the
principal in the database.

{-|+}allow_tix

The “-allow_tix” option forbids the issuance of any tickets for this
principal. “+allow_tix” clears this flag. The default is
“+allow_tix”. In effect, “-allow_tix” sets the
KRB5_KDB_DISALLOW_ALL_TIX flag on the principal in the database.

{-|+}needchange

The “+needchange” option sets a flag in attributes field to force a
password change; “-needchange” clears it. The default is
“-needchange”. In effect, “+needchange” sets the
KRB5_KDB_REQUIRES_PWCHANGE flag on the principal in the database.

{-|+}password_changing_service

The “+password_changing_service” option sets a flag in the attributes
field marking this principal as a password change service. (Again, you
will probably never need to use this option.)
“-password_changing_service” clears the flag. The default is
“-password_changing_service”. In effect, the
“+password_changing_service” option sets the KRB5_KDB_PWCHANGE_SERVICE
flag on the principal in the database.

{-|+}ok_as_delegate

The “+ok_as_delegate” option sets a flag in tickets issued for the
service principal. Some client programs may recognize this flag as
indicating that it is okay to delegate credentials to the service. If
ok_as_delegate is set on a cross-realm TGT, it indicates that the
foreign realm's ok_as_delegate flags should be honored by clients in
the local realm. The default is “-ok_as_delegate”.

-randkey

Sets the key for the principal to a random value (add_principal
only). MIT recommends using this option for host keys.

-pw password

Sets the key of the principal to the specified string and does not
prompt for a password (add_principal only). MIT does
not recommend using this option.

-e enc:salt...

Uses the specified list of enctype-salttype pairs for setting the key
of the principal. The quotes are necessary if there are multiple
enctype-salttype pairs. This will not function against kadmin daemons
earlier than krb5-1.2. See Supported Encryption Types and
Salts for available types.

-unlock

Unlocks a locked principal (one which has received too many failed
authentication attempts without enough time between them according to
its password policy) so that it can successfully authenticate.

If, on the other hand, you want to set up an account that expires on
January 1, 2000, that uses a policy called “stduser”, with a temporary
password (which you want the user to change immediately), you would type
the following. (Note: each line beginning with ⇒ is a
continuation of the previous line.)

If you will need cross-realm authentication, you need to add principals
for the other realm's TGT to each realm. For example, if you need to
do cross-realm authentication between the realms ATHENA.MIT.EDU
and EXAMPLE.COM, you would need to add the principals
‘krbtgt/EXAMPLE.COM@ATHENA.MIT.EDU’ and
‘krbtgt/ATHENA.MIT.EDU@EXAMPLE.COM’ to both
databases. You need to be sure the passwords and the key version
numbers (kvno) are the same in both databases. This may require
explicitly setting the kvno with the ‘-kvno’ option. See
Cross-realm Authentication for more details.

5.3.4 Deleting Principals

To delete a principal, use the kadmin delete_principal command,
which requires the “delete” administrative privilege. The syntax is:

delete_principal [-force] principal

delete_principal has the alias delprinc. The
-force option causes delete_principal not to ask if you're
sure. For example:

kadmin: delprinc jennifer
Are you sure you want to delete the principal
"jennifer@ATHENA.MIT.EDU"? (yes/no): yes
Principal "jennifer@ATHENA.MIT.EDU" deleted.
Make sure that you have removed this principal from
all ACLs before reusing.
kadmin:

5.3.5 Changing Passwords

To change a principal's password use the kadmin change_password
command, which requires the “modify” administrative privilege (unless
the principal is changing his/her own password). The syntax is:

change_password [options] principal

The change_password option has the alias cpw.
change_password takes the following options:

-randkey

Sets the key of the principal to a random value.

-pw password

Sets the password to the string password. MIT does not
recommend using this option.

-e "enc:salt..."

Uses the specified list of enctype-salttype pairs for setting the key
of the principal. The quotes are necessary if there are multiple
enctype-salttype pairs. This will not function against kadmin daemons
earlier than krb5-1.2. See Supported Encryption Types and
Salts for possible values.

-keepold

Keeps the previous kvno's keys around. This flag is usually not
necessary except perhaps for TGS keys. Don't use this flag unless you
know what you're doing. This option is not supported for the LDAP
database

For example:

kadmin: cpw david
Enter password for principal david@ATHENA.MIT.EDU:<= Type the new password.Re-enter password for principal david@ATHENA.MIT.EDU:<= Type it again.Password for david@ATHENA.MIT.EDU changed.
kadmin:

Note that change_password will not let you change the password to
one that is in the principal's password history.

5.4 Policies

A policy is a set of rules governing passwords. Policies can dictate
minimum and maximum password lifetimes, minimum number of characters and
character classes a password must contain, and the number of old
passwords kept in the database.

5.4.2 Retrieving the List of Policies

You can retrieve the list of policies with the kadmin
list_policies command, which requires the “list” privilege. The
syntax is:

list_policies [expression]

where expression is a shell-style glob expression that can
contain the characters *, ?, and []. All policy names matching the
expression are displayed. The list_policies command has the aliases
listpols, get_policies, and getpols. For example:

5.4.3 Adding or Modifying Policies

To add a new policy, use the kadmin add_policy command, which
requires the “add” administrative privilege. The syntax is:

add_policy [options] policy_name

To modify attributes of a principal, use the kadmin modify_policy
command, which requires the “modify” administrative privilege. The
syntax is:

modify_policy [options] policy_name

add_policy has the alias addpol.
modify_poilcy has the alias modpol.

The add_policy and modify_policy commands take the
following switches:

-maxlife time

Sets the maximum lifetime of a password to time.

-minlife time

Sets the minimum lifetime of a password to time.

-minlength length

Sets the minimum length of a password to length characters.

-minclasses number

Requires at least number of character classes in a password.

-history number

Sets the number of past keys kept for a principal to number. This option is not supported for LDAP database.

-maxfailure maxnumber

Sets the maximum number of authentication failures before the principal
is locked. Authentication failures are only tracked for principals
which require preauthentication.

-failurecountinterval failuretime

Sets the allowable time between authentication failures. If an
authentication failure happens after failuretime has elapsed since
the previous failure, the number of authentication failures is reset to
1.

-lockoutduration lockouttime

Sets the duration for which the principal is locked from authenticating
if too many authentication failures occur without the specified failure
count interval elapsing.

Note: The policies are created under realm container in the LDAP database.

5.4.5 Updating the History Key

If a policy specifies a number of old keys kept of two or more, the
stored old keys are encrypted in a history key, which is found in the
key data of the kadmin/history principal.

Currently there is no support for proper rollover of the history key,
but you can change the history key (for example, to use a better
encryption type) at the cost of invalidating currently stored old keys.
To change the history key, run:

kadmin: change_password -randkey kadmin/history

This command will fail if you specify the -keepold flag. Only one
new history key will be created, even if you specify multiple key/salt
combinations.

In the future, we plan to migrate towards encrypting old keys in the
master key instead of the history key, and implementing proper rollover
support for stored old keys.

Otherwise, the principals will not match those in the database and will
not be dumped:

shell% kdb5_util dump -verbose dumpfile K/M kadmin/admin
shell%

If you do not specify a dump file, kdb5_util will dump the
database to the standard output.

There is currently a bug where the default dump format omits the
per-principal policy information. In order to dump all the data
contained in the Kerberos database, you must perform a normal dump (with
no option flags) and an additional dump using the “-ov” flag to a
different file.

requires the dump to be in the Kerberos 5 Beta 5 and earlier dump format
(“kdb5_edit load_dump version 2.0”).

-b6

requires the dump to be in the Kerberos 5 Beta 6 format (“kdb5_edit
load_dump version 3.0”).

-b7

requires the dump to be in the Kerberos 5 Beta 7 format (“kdb5_edit
load_dump version 4”).

-ov

requires the dump to be in ovsec_adm_export format.

-verbose

causes the name of each principal and policy to be printed as it is
loaded.

-update

causes records from the dump file to be updated in or added to the
existing database. This is useful in conjunction with an
ovsec_adm_export format dump if you want to preserve per-principal
policy information, since the current default format does not contain
this data.

-hash

causes the database to be stored as a hash rather than a binary tree.

For example:

shell% kdb5_util load dumpfile principal
shell%

shell% kdb5_util load -update dumpfile principal
shell%

If the database file exists, and the -update flag was not given,
kdb5_util will overwrite the existing database.

5.5.4 Creating and Destroying a Kerberos Database

If you need to create a new Kerberos database, use the kdb5_utilcreate command. The syntax is:

kdb5_util create [-s]

If you specify the ‘-s’ option, kdb5_util will stash a copy
of the master key in a stash file. (See Creating a Stash File.) For
example:

shell% /usr/local/sbin/kdb5_util -r ATHENA.MIT.EDU create -s
kdb5_util: No such file or directory while setting active database to
⇒ '/usr/local/var/krb5kdc/principal'
Initializing database '/usr/local/var/krb5kdc/principal' for
⇒ realm 'ATHENA.MIT.EDU',
master key name 'K/M@ATHENA.MIT.EDU'
You will be prompted for the database Master Password.
It is important that you NOT FORGET this password.Enter KDC database master key:<= Type the master password.Re-enter KDC database master key to verify:<= Type it again.shell%

If you need to destroy the current Kerberos database, use the
kdb5_utildestroy command. The syntax is:

kdb5_util destroy [-f]

The destroy command destroys the database, first overwriting the
disk sectors and then unlinking the files. If you specify the
‘-f’ option, kdb5_util will not prompt you for a
confirmation before destroying the database.

5.6 Global Operations on the Kerberos LDAP Database

The kdb5_ldap_util is the primary tool for administrating the Kerberos LDAP database. It allows an administrator to manage realms, Kerberos services ( KDC and Admin Server) and ticket policies.
The syntax is:

Specifies the Kerberos realm of the database; by default the realm returned by ‘krb5_default_local_realm’ (3) is used.

-subtrees subtree_dn_list

Specifies the list of subtrees containing principals of a realm. The list contains the DN of the subtree objects separated by colon(:).

-sscope search_scope

Specifies the scope for searching the principals under the subtree. The possible values are 1 or one (one level), 2 or sub (subtree).

-containerref container_reference_dn

Specfies the DN of the container object in which the principals of a realm will be created. If the container reference is not configured for a realm, the principals will be created in the realm container.

-k mkeytype

Specifies the key type of the master key in the database; the default
is that given in kdc.conf.

-m

Specifies that the master database password should be read from the TTY rather than fetched from a file on disk.

-p password

Specifies the master database password. This option is not recommended.

-sf stashfilename

Specifies the stash file of the master database password.

-s

Specifies that the stash file is to be created.

-maxtktlife max_ticket_life

Specifies maximum ticket life for principals in this realm. This value is used, if it is not set on the principal.

-maxrenewlife max_renewable_ticket_life

Specifies maximum renewable life of tickets for principals in this realm. This value is used, if it is not set on the principal.

ticket_flags

Specifies the ticket flags. If this option is not specified, by default, none of the flags are set. This means all the ticket options will be allowed and no restriction will be set. This value is used, if it is not set on the principal.
The various flags are:

-allow_dup_skey disables user-to-user authentication for
principals by prohibiting principals from obtaining a sessions key for
another user. (Sets the ‘KRB5_KDB_DISALLOW_DUP_SKEY’ flag.)
+allow_dup_skey clears this flag.

{-|+}requires_preauth

+requires_preauth requires principals to preauthenticate before being allowed to kinit. (Sets the ‘KRB5_KDB_REQURES_PRE_AUTH’ flag.) -requires_preauth clears this flag.

{-|+}requires_hwauth

+requires_hwauth requires principals to preauthenticate using a
hardware device before being allowed to kinit. (Sets the
‘KRB5_KDB_REQURES_HW_AUTH’ flag.) -requires_hwauth clears
this flag.

{-|+}ok_as_delegate

+ok_as_delegate sets the OK-AS-DELEGATE flag on tickets issued for use
with this principal as the service, which clients may use as a hint that
credentials can and should be delegated when authenticating to the service.
(Sets the ‘KRB5_KDB_OK_AS_DELEGATE’ flag.) -ok_as_delegate clears
this flag.

{-|+}allow_svr

-allow_svr prohibits the issuance of service tickets for principals. (Sets the ‘KRB5_KDB_DISALLOW_SVR’ flag.) +allow_svr clears this flag.

{-|+}allow_tgs_req

-allow_tgs_req specifies that a Ticket-Granting Service
(TGS) request for a service ticket for principals is not
permitted. This option is useless for most
things.+allow_tgs_req clears this flag. The default is
+allow_tgs_req. In effect, -allow_tgs_req sets the
‘KRB5_KDB_DISALLOW_TGT_BASED’ flag on principals in the
database.

{-|+}allow_tix

-allow_tix forbids the issuance of any tickets for
principals. +allow_tix clears this flag. The default is
+allow_tix. In effect, -allow_tix sets the
‘KRB5_KDB_DISALLOW_ALL_TIX’ flag on principals in the database.

{-|+}needchange

+needchange sets a flag in attributes field to force a password change;
-needchange clears it. The default is -needchange. In effect,
+needchange sets the ‘KRB5_KDB_REQURES_PWCHANGE’ flag on
principals in the database.

{-|+}password_changing_service

+password_changing_service sets a flag in the attributes field
marking principal as a password change service principal (useless for
most things). -password_changing_service clears the flag. This
flag intentionally has a long name. The default is
-password_changing_service. In effect,
+password_changing_service sets the
‘KRB5_KDB_PWCHANGE_SERVICE’ flag on principals in the database.

Specifies the Kerberos realm of the database; by default the realm returned by krb5_default_local_realm (3) is used.

-subtrees subtree_dn_list

Specifies the list of subtrees containing principal objects in the realm.The list contains the DN of the subtree objects separated by colon(:). This list replaces the existing list.

-sscope search_scope

Specifies the scope for searching the principals under the subtrees. The possible values are 1 or one (one level), 2 or sub (subtrees).

-containerref container_reference_dn

Specifies the Distinguished Name (DN) of the container object in which the principals of a realm will be created.

-maxtktlife max_ticket_life

Specifies maximum ticket life for principals in this realm. This value is used, if it is not set on the principal.

-maxrenewlife max_renewable_ticket_life

Specifies maximum renewable life of tickets for principals in this realm. This value is used, if it is not set on the principal.

-ticket_flags

Specifies the ticket flags. If this option is not specified, by default, none of the flags are set. This means all the ticket options will be allowed and no restriction will be set. This value is used, if it is not set on the principal.
The various flags are:

-allow_dup_skey Disables user-to-user authentication for principals by prohibiting principals from obtaining a sessions key for another user. (Sets the ‘KRB5_KDB_DISALLOW_DUP_SKEY’ flag.). +allow_dup_skey clears This flag.

{-|+}requires_preauth

+requires_preauth requires principals to preauthenticate before being allowed to kinit. Sets the
‘KRB5_KDB_REQURES_PRE_AUTH’ flag.-requires_preauth clears this flag.

{-|+}requires_hwauth

+requires_hwauth requires principals to preauthenticate using a hardware device before being allowed to kinit. (Sets the
‘KRB5_KDB_REQURES_HW_AUTH’ flag.)-requires_hwauth clears this flag.

{-|+}allow_svr

-allow_svr prohibits the issuance of service tickets for principals. (Sets the ‘KRB5_KDB_DISALLOW_SVR’ flag.) +allow_svr clears This flag.

{-|+}allow_tgs_req

-allow_tgs_req specifies that a Ticket-Granting Service (TGS) request for a service ticket for principals is not permitted. This option is useless for most things.+allow_tgs_req clears this flag.
The default is. +allow_tgs_req. In effect,
-allow_tgs_req sets the ‘KRB5_KDB_DISALLOW_TGT_BASED’ flag
on principals in the database.

{-|+}allow_tix

-allow_tix forbids the issuance of any tickets for
principals. +allow_tix clears this flag. The default is
+allow_tix. In effect, -allow_tix sets the
‘KRB5_KDB_DISALLOW_ALL_TIX’ flag on principals in the database.

{-|+}needchange

+needchange sets a flag in attributes field to force a password change; -needchange clears it.
The default is -needchange. In effect,+needchange sets
the ‘KRB5_KDB_REQURES_PWCHANGE’ flag on principals in the
database.

{-|+}password_changing_service

+password_changing_service sets a flag in the attributes field marking principal as a password change service principal (useless for most things).-password_changing_service clears the flag. This flag intentionally has a long name. The default is -password_changing_service
In effect, +password_changing_service sets the ‘KRB5_KDB_PWCHANGE_SERVICE’ flag on principals in the database.

-allow_dup_skey Disables user-to-user authentication for principals by prohibiting principals from obtaining a sessions key for another user. (Sets the ‘KRB5_KDB_DISALLOW_DUP_SKEY’ flag.). +allow_dup_skey clears This flag.

{-|+}requires_preauth

+requires_preauth requires principals to preauthenticate before being allowed to kinit. (Sets the ‘KRB5_KDB_REQURES_PRE_AUTH’ flag.)
-requires_preauth clears this flag.

{-|+}requires_hwauth

+requires_hwauth requires principals to preauthenticate using a
hardware device before being allowed to kinit. (Sets the
‘KRB5_KDB_REQURES_HW_AUTH’ flag.) -requires_hwauth clears
this flag.

{-|+}allow_svr

-allow_svr prohibits the issuance of service tickets for principals. (Sets the ‘KRB5_KDB_DISALLOW_SVR’ flag.) +allow_svr clears This flag.

{-|+}allow_tgs_req

-allow_tgs_req specifies that a Ticket-Granting Service (TGS) request for a service ticket for principals is not permitted. This option is useless for most things.+allow_tgs_req clears this flag.
The default is +allow_tgs_req. In effect,
-allow_tgs_req sets the ‘KRB5_KDB_DISALLOW_TGT_BASED’ flag
on principals in the database.

{-|+}allow_tix

-allow_tix forbids the issuance of any tickets for
principals. +allow_tix clears this flag. The default is
+allow_tix. In effect, -allow_tix sets the
‘KRB5_KDB_DISALLOW_ALL_TIX’ flag on principals in the database.

{-|+}needchange

+needchange sets a flag in attributes field to force a password change;
-needchange clears it. The default is -needchange. In
effect, +needchange sets the ‘KRB5_KDB_REQURES_PWCHANGE’
flag on principals in the database.

{-|+}password_changing_service

+password_changing_service sets a flag in the attributes field
marking principal as a password change service principal (useless for
most things). -password_changing_service clears the flag.
This flag intentionally has a long name. The default is
-password_changing_service. In effect,
+password_changing_service sets the
‘KRB5_KDB_PWCHANGE_SERVICE’ flag on principals in the database.

5.6.11 Creating a Service Object (eDirectory)

Creates a service object in directory and assigns appropriate rights on the container holding kerberos data.

Options are as follows:

-kdc

Specifies the KDC service

-admin

Specifies the Administration service

-pwd

Specifies the Password service

-servicehost service_host_list

Specifies the list of entries separated by a colon (:). Each entry consists of the hostname or IP address of the server hosting the service, transport protocol and the port number of the service separated by a pound sign (#).
For example,

server1#tcp#88:server2#udp#89.

-realm realm_list

Specifies the list of realms that are to be associated with this service. The list contains the name of the realms separated by a colon (:).

-randpw

Generates and sets a random password. This option is used to set the random password for the service object in directory and also to store it in the file. -fileonly option cannot be used with -randpw option.

-fileonly

Stores the password only in a file and not in directory. The -randpw option can not be used when -fileonly option is specified.

-f filename

Specifies the complete path of the file where the service object password is stashed. If this option is not specified, the default file will be /usr/local/var/service_passwd

service_dn

Specifies the Distinguished Name (DN) of the Kerberos service to be created.

5.6.12 Modifying a Service Object (eDirectory)

Modifies the attributes of a service and assigns appropriate rights, if realm associations are changed.

Options are as follows:

-servicehost service_host_list

List of entries separated by a colon (:) where each entry consists of host name or IP address of the server hosting the service, transport protocol, and port number of the service separated by a pound sign (#). This list replaces the existing list.
For example,

server1#tcp#88:server2#udp#89

-clearservicehost service_host_list

Specifies the list of servicehost entries to be removed from the existing list. This is a colon separated list.

-addservicehost service_host_list

Specifies the list of servicehost entries to be added to the existing list. This is a colon separated list.

-realm realm_list

Specifies the list of realms that are to be associated with this service. The list contains the name of the realms separated by a colon (:). This list replaces the existing list.

-clearrealm realm_list

Specifies the list of realms to be removed from the existing list. The list contains the name of the realms separated by a colon (:).

-addrealm realm_list

Specifies the list of realms to be added to the existing list. The list contains the name of the realms separated by a colon (:).

service_dn

Specifies the Distinguished Name (DN) of the Kerberos service to be modified.

5.6.15 Listing Available Service Objects (eDirectory)

list_service [-basedn base_dn]

Lists the name of services under a given base in directory. Options is as follows:

-basedn base_dn

Specifies the base DN for searching the policies, limiting the search to a particular subtree. If this option is not provided, LDAP Server specific search base will be used. For e.g., in the case of OpenLDAP, value of defaultsearchbase from slapd.conf file will be used, where as in the case of eDirectory, the default value for the base DN is Root.

5.6.16 Passwords for Service Objects (eDirectory)

setsrvpw[-randpw|-fileonly][-f filename]service_dn

Allows an administrator to set password for service objects such as KDC and Administration server in eDirectory and store them in a file. The
-fileonly command stores the password in a file and not in the eDirectory object.
Options are as follows:

-randpw

Generates and sets a random password on the directory object and stores it in the file. The -fileonly option can not be used if -randpw option is already specified.

-fileonly

Stores the password only in a file and not in eDirectory. The -randpw option can not be used when -fileonly option is specified.

-f filename

Specifies the complete path of the file where the service object password is stashed. If this option is not specified, the default file will be /usr/local/var/service_passwd.

service_dn

Specifies the Distinguished Name (DN) of the service object whose password is to be set.

5.7 Cross-realm Authentication

In order for a KDC in one realm to authenticate Kerberos users in a
different realm, it must share a key with the KDC in the other realm.
In both databases, there must be krbtgt service principals for realms.
These principals should all have the same passwords, key version
numbers, and encryption types. For example, if the administrators of
ATHENA.MIT.EDU and EXAMPLE.COM wanted to authenticate
across the realms, they would run the following commands on the KDCs in
both realms:

Even if most principals in a realm are generally created with the
requires_preauth flag enabled, this flag is not desirable on
cross-realm authentication keys because doing so makes it impossible to
disable preauthentication on a service-by-service basis. Disabling it
as in the example above is recommended.

It is also very important that these principals have good passwords.
MIT recommends that TGT principal passwords be at least 26
characters of random ASCII text.

5.8 Changing the krbtgt Key

A Kerberos Ticket Granting Ticket (TGT) is a service ticket for the
principal krbtgt/REALM. The key for this principal is created when
the Kerberos database is initialized and need not be changed. However,
it will only have the encryption types supported by the KDC at the time
of the initial database creation. To allow use of newer encryption
types for the TGT, this key has to be changed.

Changing this key using the normal kadmin change_password command
would invalidate any previously issued TGTs. Therefore, when changing
this key, normally one should use the -keepold flag to
change_password to retain the previous key in the database as
well as the new key. For example:

After issuing this command, the old key is still valid and is still
vulnerable to (for instance) brute force attacks. To completely
retire an old key or encryption type, run the purgekeys command
to delete keys with older kvnos, ideally first making sure that all
tickets issued with the old keys have expired.

6 Configuring Kerberos with OpenLDAP back-end

Set up SSL on the OpenLDAP server and client to ensure secure
communication when the KDC service and LDAP server are on different
machines. ldapi:// can be used if the LDAP server and KDC
service are running on the same machine.

Setting up SSL on the OpenLDAP server:

Get a CA certificate using OpenSSL tools

Configure OpenLDAP server for using SSL/TLS

For the latter, you need to specify the location of CA certificate location in slapd.conf file.

For the KDC and Admin Server, you need to do the client-side configuration in ldap.conf.

For example,

TLS_CACERT /etc/openldap/certs/cacert.pem

Include the Kerberos schema file (kerberos.schema) in the
configuration file (slapd.conf) on the LDAP Server, by providing the
location where it is stored.

include /etc/openldap/schema/kerberos.schema

Choose DNs for the KDC and kadmin servers to bind to the LDAP server,
and create them if necessary. These DNs will be specified with the
ldap_kdc_dn and ldap_kadmind_dn directives in krb5.conf;
their passwords can be stashed with kdb5_ldap_util stashsrvpw
and the resulting file specified with the
ldap_service_password_file directive.

Choose a DN for the global Kerberos container entry (but do not create
the entry at this time). This DN will be specified with the
ldap_kerberos_container_dn directive in krb5.conf. Realm
container entries will be created underneath this DN. Principal
entries may exist either underneath the realm container (the default)
or in separate trees referenced from the realm container.

Configure the LDAP server ACLs to enable the KDC and kadmin server DNs
to read and write the Kerberos data.

Sample access control information

access to dn.base=""
by * read
access to dn.base="cn=Subschema"
by * read
access to attrs=userPassword,userPKCS12
by self write
by * auth
access to attrs=shadowLastChange
by self write
by * read
# Providing access to realm container
access to dn.subtree= "cn=EXAMPLE.COM,cn=krbcontainer,dc=example,dc=com"
by dn.exact="cn=kdc-service,dc=example,dc=com" read
by dn.exact="cn=adm-service,dc=example,dc=com" write
by * none
# Providing access to principals, if not underneath realm container
access to dn.subtree= "ou=users,dc=example,dc=com"
by dn.exact="cn=kdc-service,dc=example,dc=com" read
by dn.exact="cn=adm-service,dc=example,dc=com" write
by * none
access to *
by * read

If the locations of the container and principals or the DNs of the
service objects for a realm are changed then this information should
be updated.

Use the -subtrees option if the principals are to exist in a separate subtree from the realm container. Before executing the command, make sure that the subtree mentioned above ‘(ou=users,dc=example,dc=com)’ exists. If the principals will exist underneath the realm container, omit the -subtrees option and do not worry about creating the principal subtree.

For more information, refer to the section Global Operations on the Kerberos LDAP Database.

The realm object is created under the ldap_kerberos_container_dn specified in the configuration file. This operation will also create the Kerberos container, if not present already. This will be used to store information related to all realms.

Stash the password of the service object used by the KDC and
Administration service to bind to the LDAP server using the stashsrvpw
command of kdb5_ldap_util. The object DN should be the same as
ldap_kdc_dn and ldap_kadmind_dn values specified in the krb5.conf
file.

Add krb5principalname to the indexes in slapd.conf to speed up the access.

With the LDAP back end it is possible to provide aliases for principal
entries. Currently we provide no mechanism provided for creating
aliases, so it must be done by direct manipulation of the LDAP
entries.

An entry with aliases contains multiple values of the krbPrincipalName
attribute. Since LDAP attribute values are not ordered, it is
necessary to specify which principal name is canonical, by using the
krbCanonicalName attribute. Therefore, to create aliases for an
entry, first set the krbCanonicalName attribute of the entry to the
canonical principal name (which should be identical to the
pre-existing krbPrincipalName value), and then add additional
krbPrincipalName attributes for the aliases.

Principal aliases are only returned by the KDC when the client
requests canonicalization. Canonicalization is normally requested for
service principals; for client principals, an explicit flag is often
required (e.g. kinit -C) and canonicalization is only performed
for initial ticket requests.

7 Application Servers

If you need to install the Kerberos V5 programs on an application
server, please refer to the Kerberos V5 Installation Guide. Once
you have installed the software, you need to add that host to the
Kerberos database (see Adding or Modifying Principals), and generate
a keytab for that host, that contains the host's key. You also
need to make sure the host's clock is within your maximum clock skew of
the KDCs.

7.1 Keytabs

A keytab is a host's copy of its own keylist, which is analogous
to a user's password. An application server that needs to authenticate
itself to the KDC has to have a keytab that contains its own principal
and key. Just as it is important for users to protect their passwords,
it is equally important for hosts to protect their keytabs. You should
always store keytab files on local disk, and make them readable only by
root, and you should never send a keytab file over a network in the
clear. Ideally, you should run the kadmin command to extract a
keytab on the host on which the keytab is to reside.

7.1.1 Adding Principals to Keytabs

To generate a keytab, or to add a principal to an existing keytab, use
the ktadd command from kadmin, which requires the
“inquire” administrative privilege. (If you use the -globprinc_exp option, it also requires the “list” administrative
privilege.) The syntax is:

use keytab as the keytab file. Otherwise, ktadd will use the
default keytab file (/etc/krb5.keytab).

-e "enc:salt..."

Uses the specified list of enctype-salttype pairs for setting the key
of the principal. The quotes are necessary if there are multiple
enctype-salttype pairs. This will not function against kadmin daemons
earlier than krb5-1.2. See Supported Encryption Types and
Salts for all possible values.

-q

run in quiet mode. This causes ktadd to display less verbose
information.

principal | -glob principal expression

add principal, or all principals matching principal expression
to the keytab. The rules for principal expression are the same as
for the kadmin list_principals (see Retrieving a List of Principals) command.

Here is a sample session, using configuration files that enable only
‘des-cbc-crc’ encryption. (The line beginning with ⇒ is a
continuation of the previous line.)

7.2 Clock Skew

In order to prevent intruders from resetting their system clocks in
order to continue to use expired tickets, Kerberos V5 is set up to
reject ticket requests from any host whose clock is not within the
specified maximum clock skew of the KDC (as specified in the
kdc.conf file). Similarly, hosts are configured to reject
responses from any KDC whose clock is not within the specified maximum
clock skew of the host (as specified in the krb5.conf file). The
default value for maximum clock skew is 300 seconds, or five minutes.

MIT suggests that you add a line to client machines'
/etc/rc files to synchronize the machine's clock to your KDC at
boot time. On UNIX hosts, assuming you had a kdc called
kerberos in your realm, this would be:

gettime -s kerberos

If the host is not likely to be rebooted frequently, you may also want
to set up a cron job that adjusts the time on a regular basis.

7.3 Getting DNS Information Correct

Several aspects of Kerberos rely on name service. In order for Kerberos
to provide its high level of security, it is less forgiving of name
service problems than some other parts of your network. It is important
that your Domain Name System (DNS) entries and your hosts have the
correct information.

Each host's canonical name must be the fully-qualified host name
(including the domain), and each host's IP address must reverse-resolve
to the canonical name.

Other than the localhost entry, make all entries in each
machine's /etc/hosts file in the following form:

7.4 Configuring Your Firewall to Work With Kerberos V5

If you need off-site users to be able to get Kerberos tickets in your
realm, they must be able to get to your KDC. This requires either that
you have a slave KDC outside your firewall, or you configure your
firewall to allow UDP requests into at least one of your KDCs, on
whichever port the KDC is running. (The default is port
88; other ports may be specified in the KDC's kdc.conf
file.) Similarly, if you need off-site users to be able to change
their passwords in your realm, they must be able to get to your
Kerberos admin server. The default port for the admin server is
749.

If your on-site users inside your firewall will need to get to KDCs in
other realms, you will also need to configure your firewall to allow
outgoing TCP and UDP requests to port 88.
Additionally, if they will need to get to any Kerberos V4 KDCs, you may
also need to allow TCP and UDP requests to port
750. If your on-site users inside your firewall
will need to get to Kerberos admin servers in other realms, you will
also need to allow outgoing TCP and UDP requests to port
749.

If any of your KDCs are outside your firewall, you will need to allow
kprop requests to get through to the remote KDC. Kprop
uses the krb5_prop service on port 754 (tcp).

If you need your off-site users to have access to machines inside your
firewall, you need to allow TCP connections from their off-site hosts on
the appropriate ports for the programs they will be using. The
following lines from /etc/services show the default port numbers
for the Kerberos V5 programs:

By default, Kerberos V5 telnet and ftp use the same
ports as the standard telnet and ftp programs, so if you
already allow telnet and ftp connections through your firewall, the
Kerberos V5 versions will get through as well. If you do not
already allow telnet and ftp connections through your firewall, but need
your users to be able to use Kerberos V5 telnet and ftp, you can
either allow ftp and telnet connections on the standard ports, or switch
these programs to non-default port numbers and allow ftp and telnet
connections on those ports to get through.

Kerberos V5 rsh uses the kshell service, which by
default uses port 544. However, the server must
be able to make a TCP connection from the kshell port to an arbitrary
port on the client, so if your users are to be able to use rsh
from outside your firewall, the server they connect to must be able to
send outgoing packets to arbitrary port numbers. Similarly, if your
users need to run rsh from inside your firewall to hosts outside
your firewall, the outside server needs to be able to connect to an
arbitrary port on the machine inside your firewall. Because
Kerberos V5 rcp uses rsh, the same issues apply. If
you need to use rsh (or rcp) through your firewall and
are concerned with the security implications of allowing connections to
arbitrary ports, MIT suggests that you have rules that
specifically name these applications and, if possible, list the allowed
hosts.

The book UNIX System Security, by David Curry, is a good
starting point for learning to configure firewalls.

8 Backups of Secure Hosts

When you back up a secure host, you should exclude the host's keytab
file from the backup. If someone obtained a copy of the keytab from a
backup, that person could make any host masquerade as the host whose
keytab was compromised. This could be particularly dangerous if the
compromised keytab was from one of your KDCs. If the machine has a disk
crash and the keytab file is lost, it is easy to generate another keytab
file. (See Adding Principals to Keytabs.) If you are unable to
exclude particular files from backups, you should ensure that the
backups are kept as secure as the host's root password.

8.1 Backing Up the Kerberos Database

As with any file, it is possible that your Kerberos database could
become corrupted. If this happens on one of the slave KDCs, you might
never notice, since the next automatic propagation of the database would
install a fresh copy. However, if it happens to the master KDC, the
corrupted database would be propagated to all of the slaves during the
next propagation. For this reason, MIT recommends that you
back up your Kerberos database regularly. Because the master KDC is
continuously dumping the database to a file in order to propagate it to
the slave KDCs, it is a simple matter to have a cron job periodically
copy the dump file to a secure machine elsewhere on your network. (Of
course, it is important to make the host where these backups are stored
as secure as your KDCs, and to encrypt its transmission across your
network.) Then if your database becomes corrupted, you can load the
most recent dump onto the master KDC. (See Restoring a Kerberos Database from a Dump File.)

9 Bug Reporting

In any complex software, there will be bugs. If you have successfully
built and installed Kerberos V5, please use the krb5-send-pr
program to fill out a Problem Report should you encounter any errors in
our software.

Bug reports that include proposed fixes are especially welcome. If you
do include fixes, please send them using either context diffs or unified
diffs (using ‘diff -c’ or ‘diff -u’, respectively). Please be
careful when using “cut and paste” or other such means to copy a patch
into a bug report; depending on the system being used, that can result
in converting TAB characters into spaces, which makes applying the
patches more difficult.

The krb5-send-pr program is installed in the directory
/usr/local/sbin.

The krb5-send-pr program enters the problem report into our
Problem Report Management System (PRMS), which automatically assigns it
to the engineer best able to help you with problems in the assigned
category.

The krb5-send-pr program will try to intelligently fill in as
many fields as it can. You need to choose the category,
class, severity, and priority of the problem, as well
as giving us as much information as you can about its exact nature.

Choose the category that best describes the area under which your
problem falls.

The class can be sw-bug, doc-bug, change-request,
or support. The first two are exactly as their names imply. Use
change-request when the software is behaving according to
specifications, but you want to request changes in some feature or
behavior. The support class is intended for more general questions
about building or using Kerberos V5.

The severity of the problem indicates the problem's impact on the
usability of Kerberos V5. If a problem is critical, that
means the product, component or concept is completely non-operational,
or some essential functionality is missing, and no workaround is known.
A serious problem is one in which the product, component or
concept is not working properly or significant functionality is missing.
Problems that would otherwise be considered critical are rated
serious when a workaround is known. A non-critical problem is
one that is indeed a problem, but one that is having a minimal effect on
your ability to use Kerberos V5. E.g., The product, component
or concept is working in general, but lacks features, has irritating
behavior, does something wrong, or doesn't match its documentation. The
default severity is serious.

The priority indicates how urgent this particular problem is in
relation to your work. Note that low priority does not imply low
importance.
A priority of high means a solution is needed as soon as possible.
A priority of medium means the problem should be solved no later
than the next release. A priority of low means the problem should
be solved in a future release, but it is not important to your work how
soon this happens. The default priority is medium.

Note that a given severity does not necessarily imply a given priority.
For example, a non-critical problem might still have a high priority if
you are faced with a hard deadline. Conversely, a serious problem might
have a low priority if the feature it is disabling is one that you do
not need.

It is important that you fill in the release field and tell us
what changes you have made, if any.

A sample filled-out form from a company named “Toasters, Inc.” might
look like this:

If the krb5-send-pr program does not work for you, or if you did
not get far enough in the process to have an installed and working
krb5-send-pr, you can generate your own form, using the above as
an example.

Appendix B Copyright

Export of software employing encryption from the United States of
America may require a specific license from the United States
Government. It is the responsibility of any person or organization
contemplating export to obtain such a license before exporting.

WITHIN THAT CONSTRAINT, permission to use, copy, modify, and
distribute this software for any purpose and without fee is hereby
granted, provided that the above copyright notice appear in all copies
and that both that copyright notice and this permission notice appear
in supporting documentation, and that the name of M.I.T. not be used
in advertising or publicity pertaining to distribution of the software
without specific, written prior permission. Furthermore if you modify
this software you must label your software as modified software and
not distribute it in such a fashion that it might be confused with the
original MIT software. M.I.T. makes no representations about the
suitability of this software for any purpose. It is provided “as
is” without express or implied warranty.

Project Athena, Athena, Athena MUSE, Discuss, Hesiod, Kerberos, Moira,
and Zephyr are trademarks of the Massachusetts Institute of Technology
(MIT). No commercial use of these trademarks may be made without
prior written permission of MIT.

“Commercial use” means use of a name in a product or other for-profit
manner. It does NOT prevent a commercial firm from referring to the
MIT trademarks in order to convey information (although in doing so,
recognition of their trademark status should be given).

The following copyright and permission notice applies to the
OpenVision Kerberos Administration system located in
kadmin/create, kadmin/dbutil, kadmin/passwd,
kadmin/server, lib/kadm5, and portions of
lib/rpc:

WARNING: Retrieving the OpenVision Kerberos Administration system source
code, as described below, indicates your acceptance of the following
terms. If you do not agree to the following terms, do not retrieve the
OpenVision Kerberos administration system.

You may freely use and distribute the Source Code and Object Code
compiled from it, with or without modification, but this Source Code is
provided to you “AS IS” EXCLUSIVE OF ANY WARRANTY, INCLUDING, WITHOUT
LIMITATION, ANY WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A
PARTICULAR PURPOSE, OR ANY OTHER WARRANTY, WHETHER EXPRESS OR IMPLIED.
IN NO EVENT WILL OPENVISION HAVE ANY LIABILITY FOR ANY LOST PROFITS,
LOSS OF DATA OR COSTS OF PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES, OR
FOR ANY SPECIAL, INDIRECT, OR CONSEQUENTIAL DAMAGES ARISING OUT OF THIS
AGREEMENT, INCLUDING, WITHOUT LIMITATION, THOSE RESULTING FROM THE USE
OF THE SOURCE CODE, OR THE FAILURE OF THE SOURCE CODE TO PERFORM, OR FOR
ANY OTHER REASON.

OpenVision retains all copyrights in the donated Source Code. OpenVision
also retains copyright to derivative works of the Source Code, whether
created by OpenVision or by a third party. The OpenVision copyright
notice must be preserved if derivative works are made based on the
donated Source Code.

OpenVision Technologies, Inc. has donated this Kerberos Administration
system to MIT for inclusion in the standard Kerberos 5 distribution.
This donation underscores our commitment to continuing Kerberos
technology development and our gratitude for the valuable work which has
been performed by MIT and the Kerberos community.

Portions contributed by Matt Crawford <crawdad@fnal.gov> were work
performed at Fermi National Accelerator Laboratory, which is operated
by Universities Research Association, Inc., under contract
DE-AC02-76CHO3000 with the U.S. Department of Energy.

Export of this software from the United States of America may require
a specific license from the United States Government. It is the
responsibility of any person or organization contemplating export to
obtain such a license before exporting.

WITHIN THAT CONSTRAINT, permission to use, copy, modify, and
distribute this software and its documentation for any purpose and
without fee is hereby granted, provided that the above copyright
notice appear in all copies and that both that copyright notice and
this permission notice appear in supporting documentation, and that
the name of FundsXpress. not be used in advertising or publicity pertaining
to distribution of the software without specific, written prior
permission. FundsXpress makes no representations about the suitability of
this software for any purpose. It is provided “as is” without express
or implied warranty.

THIS SOFTWARE IS PROVIDED “AS IS” AND WITHOUT ANY EXPRESS OR
IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.

The implementation of the AES encryption algorithm in
src/lib/crypto/builtin/aes has the following copyright:

Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions are
met:

Redistributions of source code must retain the above copyright
notice, this list of conditions and the following disclaimer.

Redistributions in binary form must reproduce the above copyright
notice, this list of conditions and the following disclaimer in the
documentation and/or other materials provided with the distribution.

Neither the name of Red Hat, Inc., nor the names of its contributors
may be used to endorse or promote products derived from this software
without specific prior written permission.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS “AS
IS” AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER
OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

The bundled verto source code is subject to the following license:

Copyright 2011 Red Hat, Inc.

Permission is hereby granted, free of charge, to any person
obtaining a copy of this software and associated documentation files
(the "Software"), to deal in the Software without restriction,
including without limitation the rights to use, copy, modify, merge,
publish, distribute, sublicense, and/or sell copies of the Software,
and to permit persons to whom the Software is furnished to do so,
subject to the following conditions:

The above copyright notice and this permission notice shall be
included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.

The implementations of GSSAPI mechglue in GSSAPI-SPNEGO in
src/lib/gssapi, including the following files:

Permission is hereby granted, free of charge, to any person obtaining a
copy of this software and associated documentation files (the
“Software”), to deal in the Software without restriction, including
without limitation the rights to use, copy, modify, merge, publish,
distribute, sublicense, and/or sell copies of the Software, and to
permit persons to whom the Software is furnished to do so, subject to
the following conditions:

The above copyright notice and this permission notice shall be included
in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED “AS IS”, WITHOUT WARRANTY OF ANY KIND, EXPRESS
OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

Kerberos V5 includes documentation and software developed at the
University of California at Berkeley, which includes this copyright
notice:

Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions are
met:

Redistributions of source code must retain the above copyright
notice, this list of conditions and the following disclaimer.

Redistributions in binary form must reproduce the above copyright
notice, this list of conditions and the following disclaimer in the
documentation and/or other materials provided with the distribution.

Neither the name of the University nor the names of its contributors
may be used to endorse or promote products derived from this software
without specific prior written permission.

THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS “AS IS” AND
ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
SUCH DAMAGE.

Portions contributed by Novell, Inc., including the LDAP database
backend, are subject to the following license:

Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions are met:

Redistributions of source code must retain the above copyright notice,
this list of conditions and the following disclaimer.

Redistributions in binary form must reproduce the above copyright
notice, this list of conditions and the following disclaimer in the
documentation and/or other materials provided with the distribution.

The copyright holder's name is not used to endorse or promote products
derived from this software without specific prior written permission.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS “AS IS”
AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
POSSIBILITY OF SUCH DAMAGE.

Portions funded by Sandia National Laboratory
and developed by the University of Michigan's
Center for Information Technology Integration,
including the PKINIT implementation, are subject
to the following license:

Permission is granted to use, copy, create derivative works
and redistribute this software and such derivative works
for any purpose, so long as the name of The University of
Michigan is not used in any advertising or publicity
pertaining to the use of distribution of this software
without specific, written prior authorization. If the
above copyright notice or any other identification of the
University of Michigan is included in any copy of any
portion of this software, then the disclaimer below must
also be included.

THIS SOFTWARE IS PROVIDED AS IS, WITHOUT REPRESENTATION
FROM THE UNIVERSITY OF MICHIGAN AS TO ITS FITNESS FOR ANY
PURPOSE, AND WITHOUT WARRANTY BY THE UNIVERSITY OF
MICHIGAN OF ANY KIND, EITHER EXPRESS OR IMPLIED, INCLUDING
WITHOUT LIMITATION THE IMPLIED WARRANTIES OF
MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. THE
REGENTS OF THE UNIVERSITY OF MICHIGAN SHALL NOT BE LIABLE
FOR ANY DAMAGES, INCLUDING SPECIAL, INDIRECT, INCIDENTAL, OR
CONSEQUENTIAL DAMAGES, WITH RESPECT TO ANY CLAIM ARISING
OUT OF OR IN CONNECTION WITH THE USE OF THE SOFTWARE, EVEN
IF IT HAS BEEN OR IS HEREAFTER ADVISED OF THE POSSIBILITY OF
SUCH DAMAGES.

The pkcs11.h file included in the PKINIT code has the
following license:

Copyright 2006 g10 Code GmbH
Copyright 2006 Andreas Jellinghaus

This file is free software; as a special exception the author gives
unlimited permission to copy and/or distribute it, with or without
modifications, as long as this notice is preserved.

This file is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY, to the extent permitted by law; without even
the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR
PURPOSE.

Portions contributed by Apple Inc. are subject to the following license:

Copyright 2004-2008 Apple Inc. All Rights Reserved.

Export of this software from the United States of America may require
a specific license from the United States Government. It is the
responsibility of any person or organization contemplating export to
obtain such a license before exporting.

WITHIN THAT CONSTRAINT, permission to use, copy, modify, and
distribute this software and its documentation for any purpose and
without fee is hereby granted, provided that the above copyright
notice appear in all copies and that both that copyright notice and
this permission notice appear in supporting documentation, and that
the name of Apple Inc. not be used in advertising or publicity pertaining
to distribution of the software without specific, written prior
permission. Apple Inc. makes no representations about the suitability of
this software for any purpose. It is provided “as is” without express
or implied warranty.

THIS SOFTWARE IS PROVIDED “AS IS” AND WITHOUT ANY EXPRESS OR
IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.

The implementations of UTF-8 string handling in src/util/support and
src/lib/krb5/unicode are subject to the following copyright and
permission notice:

The OpenLDAP Public License
Version 2.8, 17 August 2003

Redistribution and use of this software and associated documentation
(“Software”), with or without modification, are permitted provided
that the following conditions are met:

Redistributions in source form must retain copyright statements
and notices,

Redistributions in binary form must reproduce applicable copyright
statements and notices, this list of conditions, and the following
disclaimer in the documentation and/or other materials provided
with the distribution, and

Redistributions must contain a verbatim copy of this document.

The OpenLDAP Foundation may revise this license from time to time.
Each revision is distinguished by a version number. You may use
this Software under terms of this license revision or under the
terms of any subsequent revision of the license.

THIS SOFTWARE IS PROVIDED BY THE OPENLDAP FOUNDATION AND ITS
CONTRIBUTORS “AS IS” AND ANY EXPRESSED OR IMPLIED WARRANTIES,
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AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT
SHALL THE OPENLDAP FOUNDATION, ITS CONTRIBUTORS, OR THE AUTHOR(S)
OR OWNER(S) OF THE SOFTWARE BE LIABLE FOR ANY DIRECT, INDIRECT,
INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
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LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
POSSIBILITY OF SUCH DAMAGE.

The names of the authors and copyright holders must not be used in
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in this Software without specific, written prior permission. Title
to copyright in this Software shall at all times remain with copyright
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Redistribution and use in source and binary forms, with or without
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Redistributions of source code must retain the above copyright
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Neither the name of KTH nor the names of its contributors may be
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Neither the name of the “Oracle America, Inc.” nor the names of
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Permission is hereby granted, free of charge, to any person
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documentation and/or other materials provided with the distribution.

THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS “AS IS” AND
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OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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WITHIN THAT CONSTRAINT, permission to copy, modify, and distribute
this software and its documentation in source and binary forms is
hereby granted, provided that any documentation or other materials
related to such distribution or use acknowledge that the software
was developed by the University of Southern California.

DISCLAIMER OF WARRANTY. THIS SOFTWARE IS PROVIDED “AS IS”. The
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This code is derived from software contributed to Harvard by
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Copyright 1997, 1998, 1999 Computing Research Labs,
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The following notice applies to src/util/profile/argv_parse.c and
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Copyright 1999 by Theodore Ts'o.

Permission to use, copy, modify, and distribute this software for
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WITHIN THAT CONSTRAINT, permission to use, copy, modify, and
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All files in libev are Copyright (C)2007,2008,2009 Marc Alexander Lehmann.

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